He may well have performed some tests on various target block times, and chose 10 minutes because it was near the ideal target block time and is easy to remember.

I think it is unlikely that a 10 minute block target time is the optimal time from purely an engineering perspective. I think it is most likely that the 10 minute target time is a compromise between being able to easily explain how bitcoin works, and the optimal target block time. I would imagine that explaining that blocks are found on average, once every 9.45 minutes would probably hinder the long-term adoption of bitcoin