Sure, they could have - it was not cheap or easy to come by, but until there's a particular reason to think that happened in this case, it seems to be speculation.

Everything about the voynicn manuscript is speculation. That is what makes it so fascinating for people.

While that's true "It was a hoax because <vanishingly unlikely thing>" kinda kills the fascination aspect for me. It's a bit of a downer.

This is true, but scholars can tell if a manuscript is a palimpsest, and they seem to be agreed that Voynich is not one.

It seems like a whole lot of material, all of which came from the same time period. Would have been a lucky find to find essentially a whole book's worth of the stuff in one place.