Before the term "revisionist historian" has come to mean "revising history for political purposes", it just meant challenging or revising the commonly-held view of a historical event.
Yeah, I knew that much. Interestingly, when I was trying to find some info on the "revisionist school" of history a few years ago, about all I came up with was holocaust denial.
It seems the deniers have co-opted that term/movement.
It seems that Steve is saying that Thanksgiving is less legitimate because it can't be traced back to Plymouth Rock in an unbroken line of unchanging tradition.* Which is an interesting contrast to those who claim that Christmas/Easter/Etc. are still ancient pagan holidays, despite their not having been celebrated as such in centuries.
*Maybe I totally misunderstand him, but that's why I'm asking for help.