yeah I don't know a lot about paints, but in piebald/ skewbald terms we would call it an odd coloured or tri, don't know what it would be in American paint terms though.
Tricolored (there's no dash) is a made-up horse term. It has always been used to describe dogs, never horses. You will never see it used in a breed registry or anything official.
If you Google "tricolored Paint," the only results you will get are for sale ads written by people who don't even know how to spell.
I'm not trying to insult the people who said he was tricolored. It's a very common mistake, but still incorrect.