Interesting you mention alt. We were in a sandbox together when someone said something like "You guys are pretty alt, aren't you" and my boyfriend noticed that comment. I just looked up alt for second life, I still don't understand how two people hanging out together could be considered alts. You mention our profiles looking the same? He registered just before I did, if that is what you mean.
ETA:
It's been taking a while for both of us to get the hang of using SL, it's the most complicated thing I have used online. I've never been on a sim before since I didn't think it would be my thing, so this is new to me. I often have the chat pop ups muted since they get in the way of my gameplay and if someone was talking to me I probably missed it.
There have been a lot of really kind folks on this site who have been very helpful and understanding of our newbie status. This took us by surprise.
ETA just confirmed with the boyfriend, I got banned first, a day later he did.