It seems to me that Rhett deliberately behaved in such a way as to impress his peers, otherwise he would not have been accepted into the company. Ali has nothing to do with it. I do not think that Rhett felt sympathy for Ali, rather, he needed her for self-assertion.
And Littlefoot would not be Littlefoot, if as if nothing had happened, he did not invite Rhett to play with the rest, saying that "adventure is yet to come." I liked this episode because the kids came up with how to expose Rhett, help him to throw off the brave image of a "lone dinosaur" and face the real cowardly himself. And after that, after Rhett admitted that he was not brave, he was accepted without his mask, as he is. This is exactly what Rhett needed, and not grown-ups helped him, but is was little dinosaurs. I think it's very cool.
