I'm not a college student, but I'm smarter than college students.
Literal
I [topic-は] college-student [copula-ではない][but-が] college-student [more than-より] head good.
Boastful casual register with 俺. ~ではない is the plain negative copula 'is not,' formal counterpart of じゃない. ~より marks the standard of comparison — 'X より Y いい' = 'Y is better than X.' 頭いい (from 頭がいい 'smart,' literally 'head good') has its particle dropped, typical of casual speech. The sentence has a braggy, competitive tone.