That first bear scratching looks fresh too.... Our black bears aren't really predators, they scavange and eat berries mostly. But I'm still not sure how the horses would respond to a close encounter! We try to talk loud when we are in real dense areas that look 'bear-y'. I don't want to come around a corner and be surprised by one. Maybe the horses would recognize it as a threat and bolt, maybe they'd not think it was anything other than a dog. Probably the former :~D
Years ago, I rode with Bob around the edges of "Wolf Haven", a wolf refuge here that has huge 40 acre pens for whole packs of them and they are semi wild. As we rode right along the chain link fence, wolves followed from the inside, cautiously moving through the trees, almost letting us see them but not quite. The horses knew they were there but I don't think they recognized them as being different than a dog. We've raised them with dogs and upset the natural instinct where at least ~that~ predator is concerned.
I've heard that some people wear bells when walking in bear country. It might help, but then again, it might just cause a lot of bears to have bells in their poop. ;o)