He probably isn't cause if so wouldn’t we see that? We know Aang is the last airbender so he cant be a air nomad. He probably wouldn't be fire nation. I am sure he wouldn't be a earth bender cause of his beliefs and personality and that leaves us to waterbenders which is likely but i don't think so. This is imo ofc

Eh idk

No, he wasn’t. He said he was a nonbender.

I agree @Aang on a sec, though it may have seemed like he was able to bend, he just knew alot about the spiritual side of bending.