Your efforts were admirable, but they ended up not being enough to save the baby bird, probably. There is no definite answer there, however. Who knows who exactly that large bird was. Maybe it took the baby bird to the top of a comfortable tree. Maybe it took the baby bird to a lovely nest. Maybe it took the baby bird to its belly to be digested. Maybe it just dropped the baby bird from an unreasonable height.
There is really no telling.
You tried, however. Sure, you put a rock on a bird to keep it warm. That was weird, but you tried and that is more than what most bears can (probably) say.