This comes off as sour grapes to me. Like you can't believe this guy matched in neurosurgery honestly while everyone else had to settle for something else, and it has to be because someone called in a favor.
First off, the vast majority of all med students match in IM, EM, anesthesiology, etc. regardless of how smart they are; it's by choice, because it's what they're interested in. Neurosurgery is a peculiar specialty that not many people are truly interested in. It's not like all the smartest people go into neurosurgery, the next smartest people go into Y, then Z, then IM, EM, anesthesiology, etc. Your other classmates probably matched to much "better" residency programs in their specialties than this guy did in neurosurgery as a DO.
Connections are really important, but by and large they're professional connections made through research, hard work, and following instructions, not personal connections. I would be shocked if a private practice neurologist had any influence on a neurosurgery program director in the US unless they're related. The kind of personal connections that carry weight in neurosurgery are like when you're the son of a chairman, or your brother is a senior resident at the same program, or your grandfather trained the current chairman. These people definitely match at "better" programs than similar applicants without connections do, but they only represent a small percentage of applicants.
I don't think it's fair or healthy to hold his test prep against him. It's a tough pill to swallow, but your frenemy probably worked hard and excelled in med school.