I've never seen reason to doubt it. Early paleontologists thought that they crawled around like lizards, and we know that was wrong. This is the next step. I mean, they've even found cells specific to feathers in stone, some micro-fossils.
I believe the fossil you're talking about is Microraptor? This creature had obvious feathers and well-developed wings. It was so well preserved that some of the individual cells on the plumage were found. This is an obvious bird - not a transistion