That was my first thought!
My only issue with the new update is: if this is from the first film, what scene would they have been filming? There were no scenes with paintings/setting like that in the first one :/
Is it possible that the background has nothing to do with what was filmed? Maybe, but it just seems too specific of a setting that it couldn't have doubled for anything we saw in the film.
Easy explanation: it was probably just a photo taken in waiting in a random room adjacent to one of the locations they used for a set. Or perhaps it was taken at a costume fitting. Any number of simple explanations could suffice.
I still have a feeling Webb will write the explanation for the suit change into the film. I also have a feeling that the stunt double was originally telling the truth yet, knowing the secrecy surrounding comic book movies, they want to keep everything they can under wraps so they had him recount his tweet to throw everyone off.
To your last statement, that's exactly what I feel. I get the feeling it is exactly what he said it was originally and that the "update" was a coverup of sorts. I just can't see this being an old BTS shot. There was nothing similar to this in the film, and the "off the set" stuff usually just looks a little more...industrial? Not like a fancy art room. Again, I could be wrong, but my spidey sense is tingling.