Apparently this is largely a myth, somebody did try it on a single occasion but it doesn't actually work to spread smallpox. That guy was clearly an arsehole, but yeah, apparently it wasn't a thing. I don't know how important this is given the near total genocide of the Native Americans, but it's funny how some things become "common knowledge" and some things never really get out. Soap made of Jews is another one - it was apparently an urban legend at the time due to the letters written on the rationed bars of soap. Again, more than enough evil to go around without the soap. It does seem that one insane commandants wife collected people's tattooed skin and likely did make a lampshade out of human skin. People say that didn't happen, but there's a pretty convincing photograph out there of all the seized items at one camp. Can't remember why I started talking about this, think I was trying to distract myself from a stomachache.
the fact that in an era with relatively few records, there is a recorded intentional attempt to spread smallpox (even if incompetent) is plenty to assert that the Europeans intentionally spread smallpox
edit: the CDC does say contaminated bedding can spread smallpox. reconsider the sources telling you it's a myth