Yes, exactly, that's why he's 130 IQ (okay, probably a bit more) and not 150 IQ. While 130 IQ wouldn't ordinarily be good enough to get into MIT for a non-affirmative action applicant, he's the son of two prominent Stanford professors. They will have encouraged him to have academic interests and given him all the resources to appear precocious during his teenage years - research during high school is an obvious way his parents could have burnished his college application, and most research doesn't require especially high levels of intelligence, particularly at the lab assistant level that a high schooler would be employed at. Easy enough for his parents to call in some favors to get his name added to a paper. In a pinch, SBF probably indicated somewhere on his application who his parents are - not in a bombastic way, but something that the application committee would pick up on. Academics at HYPS-level schools tend to help each other out.
As for Jane Street, it is a hard place to get into, but MIT is one of the few places where there's an established interview pipeline, which definitely makes it possible for a non-genius to have some a chance of passing. Before Cracking the Coding Interview, it was much harder to learn how FAANG interviews worked ahead of time - same thing applies.
Saying that SBF is "average", if that means 100 IQ, is ludicrous, but SBF is merely very bright, not a genius.
