Was the Boston Tea Party actually carried out by tea smugglers who wished to gain market advantage?

That is an extremely simplistic take, but without looking into the source as quoted I can't speak to whether or not Gladwell is taking a smaller point made in the citation a little too far.

From the first, one of the main elements of the resistance to the duty was to abstain entirely from drinking tea from any source; hardly the behavior of market manipulators. A participant in the Tea Party, Samuel Cooper, mentions this abstention in his account of the act.

The Boston Tea Party, like all of "the troubles" leading up to the War for Independence, was a single expression of a complicated spectrum of political resistance. In particular, the dumping of the tea was the result of several other attempts to keep the tea from being unloaded onto American soil, which itself was connected to resistance to the Tea Act of 1773. The Tea Act, in short, was an effort by the British government to give a favored status to the British East India Company, and allowed them to recoup losses they had taken in India by waiving an export duty on tea shipped to the Americas, and to allow the Company to sell their tea directly to merchants in the Americas (called "consigners" or "consignees"). A byproduct of this relationship was that the EIC was granted an effective monopoly on the importation of tea, and the waiver of the export duty from England meant that the consignees could undercut smuggled tea. Smugglers were a factor, but one of many, and hardly the only concern. However, there were also legitimate tea merchants who still had to pay import duties, and the EIC's monopoly was damaging to their businesses as well.

The expectation of the crown was that, the tea being cheaper, would still be purchased because people would naturally buy the less expensive goods, and would ignore the smugglers. And thus, even though the tea was less expensive, Americans would buy more legitimately imported tea, and pay a 3p tax per pound. This was not a universally beloved plan, by the way, and members of parliament and other British writers were wary of provoking anger from the American colonists by retaining the tax, even if it was somewhat obfuscated.

The scheme was not exactly hidden, and patriot groups like the Sons of Liberty immediately organized against it. The focus of their anger was not necessarily the tax itself - as, again, the tea was actually cheaper because of this scheme - but the lack of their voice in the decision, and the clear favoritism shown to the East India Company above the colonial markets. "No taxation without representation," in other words.

EIC ships were turned away from ports in the rest of the colonies before they could offload their cargo, but the Governor of Massachusetts, Thomas Hutchinson, refused to give in to popular pressure and refused to allow the British ships to return to England (at issue here was the payment of import duties to the colonies, different than the waived export duties owed to England - Hutchinson's sons and some of his friends were consignees of the tea shipment, and not only would the colony lose the import duty payment, but also the potential income from the sale of the tea. He had a lot to lose, personally, in both real and political terms). When several ultimatums had come and gone, a general meeting of citizens at the Old South Meeting House broke up with "a general huzza for Griffin's wharf."

The rest of the story is fairly familiar: men dressing like Mohwaks and bearing tomahawks, pitching the tea into the harbor, etc. There are a few details I think are pertinent to your question, though. There were several attempts by local Boston citizens to "rescue" tea and save it for personal use. From an account by participant George Hewes:

During the time we were throwing the tea overboard, there were several attempts made by some of the citizens of Boston and its vicinity to carry off small quantities of it for their family use. To effect that object, they would watch their opportunity to snatch up a handful from the deck, where it became plentifully scattered, and put it into their pockets.

One Captain O'Connor, whom I well knew, came on board for that purpose, and when he supposed he was not noticed, filled his pockets, and also the lining of his coat. But I had detected him and gave information to the captain of what he was doing. We were ordered to take him into custody, and just as he was stepping from the vessel, I seized him by the skirt of his coat, and in attempting to pull him back, I tore it off; but, springing forward, by a rapid effort he made his escape. He had, however, to run a gauntlet through the crowd upon the wharf nine each one, as he passed, giving him a kick or a stroke.

Later,

Another attempt was made to save a little tea from the ruins of the cargo by a tall, aged man who wore a large cocked hat and white wig, which was fashionable at that time. He had sleightly slipped a little into his pocket, but being detected, they seized him and, taking his hat and wig from his head, threw them, together with the tea, of which they had emptied his pockets, into the water. In consideration of his advanced age, he was permitted to escape, with now and then a slight kick.

and still later, protestors had to deal with floating bricks of tea by smashing it up:

The next morning, after we had cleared the ships of the tea, it was discovered that very considerable quantities of it were floating upon the surface of the water; and to prevent the possibility of any of its being saved for use, a number of small boats were manned by sailors and citizens, who rowed them into those parts of the harbor wherever the tea was visible, and by beating it with oars and paddles so thoroughly drenched it as to render its entire destruction inevitable.

These don't seem like the actions of smugglers. I can't argue for the macroeconomic results of the Tea Party, but this is an extremely well-documented event and very little of that documentation is focused on supporting the smuggler's economy: all of it is expressed on its face as attempts to resist and break the exercise of unrighteous power.

Two books that give a detailed account are both about Samuel Adams, and as a result are a little myopic with regard to his role, but are good reading nonetheless. William and Lilian Fowler's Samuel Adams, and John Alexander's Samuel Adams: America's REvolutionary Politician are both somewhat recent and have fairly thorough explanations of the Tea Party.

George Hewes' Full account can be read here

And there are a good deal of other personal accounts available through the somewhat dated website of the Boston Tea Party Historical Society