Depends when he's talking about, but yes, there's some truth to it.

Let's start at the beginning - Europe just after the collapse of the Western Roman Empire. At this point, you now have lots of "barbarian" peoples running around Europe. Most of these have been fighting against Rome (and at other times for Rome, and also against each other - it's quite complicated) for a long time. Bear in mind these ethnic groups often had very little political unity prior to the migratory period, which makes fighting wars difficult. So they often appoint one (or more rarely more than one) military leader as a king to unite the war effort.

Kingship at this stage is in theory temporary and elective, and over a population rather than a territory. But this starts to change. For a start, the barbarians start to settle in particular areas long-term (the Visigoths in Iberia, the Franks in Gaul/France, etc). On top of that, kingship increasingly concentrates around a few families, and your change at being elected king increasingly depends on the prestige of your family - "Hey, your dad and great-uncle were pretty good kings, maybe you'll be a good king too!". Guys who used to be military officers for a particular branch of the barbarian army gradually change to becoming governors (like kings, chosen based on family prestige) for a part of the now territorially-defined kingdom. Gradually "traditions" develop about who succeeds to the throne or subdivisions (ruled by dukes, counts, etc) which become laws. The most prominent example of this is the Capets of France - each Capet king, during his reign, appointed his eldest son as junior co-king to guarantee there wouldn't need to be a full election when he died. Eventually, father-to-son succession became de jure.

Now we've essentially got to the classical feudalism stage which isn't a million miles from Game Of Thrones - various lords, some small and some large, who each have their own keep and demesne (territory) which is theirs to rule, and their own personal armies. Nominally they're all bound to serve the king, though how much they actually do changes from time to time. To complicate matters a bit more, there's also the question of obligations to the Pope and Church, and on top of that, the Holy Roman Emperor is, in theory at least, set above all other kings.

So far, I'd say the answer to your question, on the whole, is yes, but then feudalism starts to fade out a bit. There are various reasons for this, but perhaps the most relevant for what we're talking about is the military revolution - military technology advancements, most notably the development of gunpowder-based weaponry, render the old feudal military model practically obsolete, and centralised armies become the norm.

From here on, the nobility still stick around as an important factor for a while, but they're not really warlords any more. OK, they can sometimes stir up local discontent and lead rebellions, or use their money to pay for mercenary armies, but they don't have personal knights and levies obligated to fight for them who they can call up when they want them any more.

Instead, they have to settle for being politicians and officials. Which they do for a while, but their world is going to come crashing down come 1789 in France.... but that's another story, of course.

I admit this isn't really my area of expertise, but I hope that'll do as a starter, and maybe some medievalists can provide more detailed answers, and correct my likely inaccuracies!

Sources: David Priestland, Merchant, Soldier, Sage (2012)