될 사람이 됐다고 생각한다 is a well-written Korean sentence. This is a compound sentence composed of (1) 될 사람이 됐다 + 고 (particle for quotation) + (2) (나는) 생각한다 means "I think the person who had been supposed to become got it. '되다' is translated as 'become' often but in this case, with the little ㄹ (an adnominal ending for "future"), it gets to mean "a person who was supposed to become (who was deserved)". The verb '되다' means 'become' often but it is used to mean sort of "turn out well, succeed" as well.

Actually it doesn't make alot of sense, doesn't seem like a native korean either... either way, broken down it's 될(be) 사람이(person) 됐다고(became) 생각한다(think) . I think I became a person to be. Nonsense