He came from a well known POA breeder originally, but his 2nd owner and the lady I bought him from, said they said he wasn't a POA. She said she felt he probably was, but they didn't want people to be aware their top stud threw solids and so they claimed he wasn't a POA. I don't think he looks like one myself.
He looks kind of like a Kentucky/Rocky Mountain horse. They tend to be small, stocky horses - often more "pony sized". A co-worker at the farm I used to work at had one named Timmy that looks very much like your pony - Timmy was about 13 hands even.
He does look like the Icelandic in that picture. I confess I don't know my pony breeds well at all, in fact I'll probably be posting a picture of my son's pony to have you all take a guess at. I don't know much about Icelandics, other than I have always seen them to be very heavy in the mane/tail/feathers department, which your pony doesn't seem to be so much, and also very heavy skelatal frame which your pony does seem to have. What is his gaiting movement like? More of a walk gait or trot gait, or more pacing, racking? I am guessing that's what the third picture you have posted of him is.