Ok, here is a rather stupid question... I don't actually understand that 'Matthew will be appearing in the 6th season of CG' screenshot :/ The season that's gonna air next month is S5, right (in which he will be appearing)?? Is he gonna appear in 2 episodes? Is that what that means?

There are no stupid questions! :D

Yes, the episode he just shot and will be in is part of season 5. What that question meant was whether they’d have him back in the future (as far as I am aware, it is not confirmed yet that CT will actually get renewed, I read that it’s a 50/50 chance at this point). But I guess that if they do get a season 6, he will be back, so it might be a recurring role. Unless Bob was really mean and it was a joke (which I actually doubt).