The particular Indians that Darby Field met refused to go to the top, and didn't know anyone who had. No artifacts have been found high on the mountain. That doesn't mean that nobody had been there before, just that any such thought is pure speculation. Members of some other tribe could have been there or somebody had climbed it but was afraid to tell his tribe and accept blame for any bad luck. Given thousands of years of human habitation, I would think somebody had been there.
The Watermans' emphasis was on the fact that only a few years after Plymouth Colony was founded, this guy made a trek into an unknown region and climbed a mountain that no information was available for - quite the adventure whether he was first or not. He was not a government-sponsored explorer or a mineral prospector or a real estate promoter, but rather the first known Boston peakbagger They also speculated on his route.
Excellent talk by Allen Koop in Candia on Tuesday night. Pretty much as Roy recalls, although Allen speculates that Field may have ascended Mount Washington in June 1641 rather than June 1642, which was the month and year that Mass. Gov. John Winthrop's summary was published. Although Winthrop was the first identified source, another earlier source, and probably the intermediary between Field and Winthrop, was found much later in written materials recovered in the U.K. (Field was illiterate and unlikely conferred directly with Winthrop; the intermediary source was someone based in Saco who met Field before and after his adventures). The Winthrop summary is quoted in Wikipedia.
http://en.wikipedia.org/wiki/Darby_Field
Also, Allen provided much interesting speculation about Field's route, which for hundreds of years was believed to be from the east (i.e., Pinkham Notch), but a reading of Winthrop's account makes more sense if Field ascended from the south, either along the southern Presi peaks (later the Crawford Path) or Montalban ridge (over Mount Isolation). The southern Presi route makes much more sense to me, as Montalban would have been the mother of all White Mountain bushwhacks. Also, references by Field to lots of snow in June seem reasonable, as 1641 (and 1642) were in the heart of the Little Ice Age when Boston Harbor was frozen solid, etc.
Whether or not native Americans ascended Mount Washington before 1641 most likely will never be known, unless a third source materializes in which Field credits his guides with having made earlier ascents. Just as we still await the finding of Mallory's camera.