Clearly not him. He initially dismissed Bitcoin and jumped on the bandwagon when it started making headlines due to its fast rising price. Plus, Adam Back seeks fame, he would happily claim to be Satoshi if it was really him. He was even criticized early on for seeming to take too much credit for Bitcoin[0].

My guess is that it's someone who was not particularly well-known prior to Bitcoin.

[0] https://bitcointalk.org/index.php?topic=225463.0