Here's what the person claimed:
Hallowe'en is traditionally a non-event here in England, because our population is overwhelmingly atheist or agnostic.
But how Hallowe'en is "celebrated" elsewhere in the world is weird. Imagine if you celebrated Christmas Eve, but then completely forgot or ignored the significance of the day after Christmas Eve, the 25th December! Let me explain....
The name Hallowe'en is an old contraction of All Hallows' Evening.
Hallow means "Holy one" (implying someone who is/was Saintly) and the e'en of Hallowe'en is from the Old English contraction of the word "evening" in its context of meaning "the day before".
Hallowe'en (All Hallows' Evening) is just the day before All Hallows' Day, which is the 1st of November.
The 1st of November is an actual Christian day of solemn celebration of all Saints of the Christian religion and is known as All Saints Day, All Hallows' Day or Hallowmas.
The whole ghosts, ghouls, witches, costumes and pumpkins thing really has nothing to do with the true Hallowe'en either. That all originates from the Christian and corporate America reinvention and rebranding of the ancient Celtic-Pagan festival of Samhain, as both a way to persuade non-Christians into their churches, and for businesses to make money out of a completely ficticious and remanufactured "holiday" event.
I forgot to mention the 2nd of November; All Souls' Day - the day which Christians commemorated all deceased people who were not Hallowed or Saints.
All Souls Day was traditionally the day after All Hallows' Day. All Souls' Day was also a day for the poor to go knocking on wealthier people's doors for donor gifts of "Soul Cakes" (a kind of biscuity scone like cake) in exchange for prayers for deceased loved ones souls.
Undoubtably, this "Soul Cakes" thing has its origins from the Scottish Pagan tradition of Guising (from "disguising") oneself in a disguise, then asking for gifts of food in exchange for a trick came from. They wore disguises in order to blend in with stray spirits. This Scottish tradition over time evolved into Trick Or Treating when Scots migrated to America, taking their pagan tradition with them. Scots still call it Guising today.
In Ireland, there was also a Pagan tradition of carving Jack O'Lanterns from turnips at Samhain. No, not pumpkins, because pumpkins were not natively found in Ireland. Irish immigrants to North America's east coast could not find turnips there, so they continued their Jack O'Lantern tradition by carving the pumpkins they found there instead.
So basically, the American version of "Hallowe'en" has stolen the Irish and Scottish pagan traditions of Samhain, then used these in combination with the Christian Hallowe'en name, the day which precedes both All Hallows' Day and All Souls' Day.
Is there any truth to what this person said?
Please see my previous answer on the origins of Halloween. That will give you a better history of the evolution of Halloween and its relationship to Samhain. See also my answers on the history of Halloween in England; Halloween's relationship with Día de Muertos; and the history of pre-Christian quarter days in Ireland (of which Samhain is the most famous).
To briefly refute the claims made in the quotation...
The whole ghosts, ghouls, witches, costumes and pumpkins thing really has nothing to do with the true Hallowe'en either. That all originates from the Christian and corporate America reinvention and rebranding of the ancient Celtic-Pagan festival of Samhain, as both a way to persuade non-Christians into their churches, and for businesses to make money out of a completely ficticious and remanufactured "holiday" event.
This is false on all counts. Ronald Hutton makes a convincing case in Stations of the Sun: A History of the Ritual Year in Britain that there is no evidence in early medieval Irish literature to suggest that Samhain had any particular associations with the dead. These came later with the celebration of All Saints' Day on Samhain. (Note that Samhain is 1 November, just as All Saints' Day is, not on 31 October like Halloween.)
The idea that Samhain was "rebranded" as a Christian holiday in order to entice pagans to come to church is completely insupportable. I've written previously about the gradual and peaceful Christian conversion of Ireland in this post. All Souls Day was originally celebrated in April in Ireland before moving to November in order to follow the Papal custom established during the Carolingian period. This was long after all of Ireland had entirely converted to Christianity.
Undoubtably, this "Soul Cakes" thing has its origins from the Scottish Pagan tradition of Guising (from "disguising") oneself in a disguise, then asking for gifts of food in exchange for a trick came from. They wore disguises in order to blend in with stray spirits.
There is no evidence that guising is a pagan tradition. Furthermore, the idea that soul cakes must be pagan in origin is refuted by the fact that there was nothing about ghosts in the original celebration of Samhain. See my linked answer on Halloween in England for more on soul cakes.
In Ireland, there was also a Pagan tradition of carving Jack O'Lanterns from turnips at Samhain.
There is no evidence that carving neep lanterns was originally a pagan practice. This sort of thing does not survive in archaeology, and the first recordings of Irish folklore in this level of detail are almost all from the late modern period. We can't prove one way or the other whether this was a pagan thing. And believe it or not, Christians sometimes -- nay, often -- invent their own folklore! No pagan starting kit needed!
So basically, the American version of "Hallowe'en" has stolen the Irish and Scottish pagan traditions of Samhain, then used these in combination with the Christian Hallowe'en name, the day which precedes both All Hallows' Day and All Souls' Day.
You can't steal a holiday which is already yours. Irish emigrants brought their holiday with them, in all its syncretic Samhain/All Saints' Day glory, when they came to the United States in droves in the 19th century. Sure, the holiday has been commercialized in ways which distance it from its "original celebration" -- but which "original celebration" would you mean? The pagan Samhain, which was a major time for political meetings in early medieval Ireland? All Saints' Day, which hundreds of millions of Christians still celebrate around the world in tandem with Halloween? The whole premise here is faulty.