He doesn't look skinny to me, he looks like he just needs muscle. I can't see his ribs or anything. I think you should just give him some time to settle in, with lots of hay and see if he gets to where you would like him to be. If not, address the issue again.
passion is when you put more energy into something than is required to do it. it is more than just enthusiasm or excitement, passion is ambition that is materialized into action to put as much heart, mind, body and soul into something as is possible. // <3 starlite - dream - lady - georgia