All I think of when I read this and see the picture is Kenai and Koda, lol, and start humming Phil Collins songs.
But anyways..
1. You said he was given a Spirit but not the spirits memories. Memories are of the spirit and as a general rule its impossible to completely erase them. Suppress and such, yeah, but they're still there unless the Spirit's been wiped blank and is just a mass of Astral. So how does the spirit not possess the memory anymore?
2. Where do the spirits come from? Ties into the first question.
3. Animals technically already have a spirit in terms of Astral. That's how there are animal spirits and guides. But elaborate ?