Supply the missing premise that makes the conclusion follow logically: P: D–most–BP: ?C:B–some–C

First day learning/studying the LSAT and ironically this is the only question on daily drills I got correct. Was my thinking spot on or did I just get lucky? Kelly (D) is mostly Caucasian (B) —— Caucasian (B) people are sometimes cool (C) — thus, it is inferring that Kelly (D) must be cool (C) (otherwise why would they be bringing this up), so therefore the answer is D —> C. Is this the proper way of interpreting this or did I just get lucky and this mode of thinking won’t help me big picture? Thank you!