Came from a known food source, edible birds. That's what they smelled and, perhaps thought they'd find some meat in there with all those feathers.
Short story:
A few summers back I had a job where I was promoting bear safety and was participating in an outdoor display complete with bear pelts and a few mounted specimens. There were resident elk in the community and they showed up, at least a dozen cow/calf pairs, on a lawn about eighty feet away. At some point the breeze shifted and suddenly there was some strange noise coming from the group. Colleagues and I looked over at the elk and they were now huddled up, calves in the middle, looking at us and barking at us and the dead bear remains we had on display. We suddenly questioned our safety but the elk decided there was more grass down the street and moved on. Even dogs barked at these items when we had them out, as though they were a live threat.
Scent remains long after we think we've eliminated them. I'm guessing the bear thought the feathers might indicate food. Their smellers work really good.