I like this story.

But it seems there some equivocation or similar confusion around here:

if any painting has an equal chance of being a Pablo, then seeing this painting doesn't tell us anything--it can't count as evidence either way.

If I know nothing about Pablo's methods and so can't tell whether any painting is a Pablo painting, why should I expect that seeing a genuine Pablo painting will tell me anything. Particularly since it seems like I already learned something from this painting - I don't understand Pablo's methods.