He does look like a dwarf to me. Several things to remember here. Both his sire and dam should and must be, kept out of the breeding pool FOR EVER.
Dwarf Minis can become incredibly expensive to keep, due to their many ongoing problems and vet care. Different types of dwarf Minis, require different care.
Here is a site you should see and read thoroughly. Dwarf Horses
And another which will break your heart. Our "Special" Friends
Dwarf minis are cute but cute is not enough. Many are sold to unsuspecting buyers for large sums. Many end up in rescues. Others live a horrific life, due to their problems. Most owners cannot successfully keep them alive and comfortable for long.
If you breed and produce a mini, it is up to the breeder, to do the right thing by the dwarf he/she has produced. Many Mini Horse lines have dwarfism in them. It is no disgrace for one's stock to have produced one. The disgrace is only if the breeder is not willing to keep and take care of that horse for its lifetime and not selling it on to an unsuspecting purchaser. And of course, not breeding again, the sire and/or dam who has produced swarfs in the past.