Gruber was mostly right, although the word "stupid" is probably not what he meant. But the fact is that whoever believed it wasn't a tax, it wouldn't raise rates, it wouldn't force you to change plans and possibly doctors, etc., was ignorant. Not stupid, necessarily, but ignorant. That said, someone who is ignorant and thinks that he actually knows these things is kinda stupid. So all the news folks, for example, who said that what Republicans said about the ACA were lies ... they were stupid.
The fact is that almost everything the GOP said about the ACA was true. Federal funding of abortions, subsidies for illegals, massive government control defined at a later date by an administrator and not Congress, death panels, increased taxes and premiums, decreased choice ... all of it was and is true.