Yeah I think its pretty clear that ARTPOP is not the 3rd single. The way Jimmy introduced her made it sound like this was to promote the tour. That combined with the G.U.Y. video being filmed (and possibly Venus too).
Why would she perform the 3rd single when it's not even announced or ready yet? Talk about premature. They're just trying to keep the era from being completely forgotten while they buy some time.
Is that now that's the excuse the Monsters are going with?