Could've been an admin. I have a plugin on my server where I can remove any block placed by anyone merely by damaging it once. So basically, I can turn it on, whip out my Thompson, and blast your base into non-existence in a matter of seconds with no trace left behind. Otherwise, he just got raided the old fashioned way.
I know the admin on this server and she did not do it and she is the only one with admin privileges. I consider myself good at raiding, but was unable to get into his house. The salvage hammer had no effect on his walls that I could get to. I even managed to get onto his ceiling and none of my tools would effect it also. It is also a bit funny as he was also the only one who was raided. Usually from my experience someone who is hacking goes around and does more damage to more than just one person.