There's a saying, "개천에서 용났다", which means to say that someone who is of low birth has become very successful." "용됐다" means the same thing. We use this term, as a compliment, to show that we're surprised to see the successful result they have made. Mostly, it is used for those who are quite unlikely to go to success and have actually attained to it, which is what surprises us.

i got it~ thank you~

용=dragon But if 용 is used in an expression such as '누구(somebody) 용 됐어.', the sentence means 'Somebody has become really beautiful or handsome comparing to the somebody in the past'