And he truly did operate at the staff level -- I know because eng levels at Meta are private. As he was climbing the ladder, people who worked with him assumed he was already a Staff Engineer, and were shocked when they realized he was 1 or 2 levels lower than that (this info would come out during perf review season).
Seniority is generally about how much people can trust you in the team, to identify blockers, provide feedback, or plan a roadmap. You can call it politics, but no one on the team would have denied that this engineer was hugely impactful. We're trying to capture these lessons + case studies in Taro.