He's being far more cooperative than, say, Liebermann was while passing the ACA, and his actual goal is to say he's fighting those out of control big city liberals by keeping the filibuster, but the changes he'll allow will make it completely different and more or less how it was in the 90s.
Sinema also wants to keep it and seems to actually be a true believer, which is dumb and not even what her voters want, so who knows what's up with that.
I don't think we can be too charitable towards Manchin considering his other stances. That said, you raise a good point: changing the filibuster doesn't really change his position; he's still an essential vote to pass any legislation in a tied senate, so he benefits from either outcome. I suppose, all other things being equal, it makes sense for him to nominally oppose ending the filibuster for the sake of his base.
The bit about Manchin is fact, though. They can't change the rule without him, and he doesn't want to eliminate the filibuster. He did say that he would consider modifying it to make it more difficult, however.