The Fresno Bee reports that "a local attorney is asking the state Attorney General's Office to investigate whether it is proper for the Fresno Metropolitan Museum to sell off its collection to satisfy its debts."
At this point, that's all it is: a request, by a private citizen, to investigate something. The requester's argument is basically the "public trust" argument: the museum, "in being granted nonprofit status, agreed that its assets were public and would be used for public purposes. If the museum ever dissolved, ... its assets should continue to be used for a public purpose. That would mean ... transferring the items to another public charity such as the Fresno Historical Society or the Fresno Art Museum."
Note that this argument would apply not just to the art, but to all the other assets of the museum -- computers, chairs, and holiday decorations.
More importantly, it's just not the case that being granted nonprofit status means you agree your "assets are public." Think of every church, hospital, private school, etc. Their assets do not "belong" to the public.