...I'm just saying it would have been more accurate (and a slightly more economical use of 140 characters) for him to say that he's going to be filming a role in A Muppet movie.1
And because I'm an equal opportunity snarker, I'll point out that it's "fortnight," not "fornight." It's a term that we don't use often in the US (more's the pity) but still, misspelling it ruins the joke.
1Speaking of which, the current working title is The Muppets...Again, which is slightly better than The Muppets 2, but only slightly. Also, they're talking about Tina Fey for the third lead, which wasn't what I had in mind, but I approve.