Opinions differ one whether a unregistered pony/horse meeting the height requirements for a mini is really considered a mini. A mini must be 38" or under no matter what, otherwise it is unregisterable. That does not mean it is not a mini though. If I have a mini and it exceeds 38" in height, they pull my registration papers on this horse, but it does not mean it still is not a miniature horse.
Now looking at that boy, I would say he looks more like a sheltand than a mini, IMO. Pretty boy and as long as he does what you want then who cares what breed he technically is!
You know how to make a miniature horse even smaller? Leave them in the dryer a little longer!
"Don't ever regret something that once made you smile"