Real users are not deleted for rule violations in most cases, suspension is usually the harshest punishment that is used. This does not extend to fake accounts that are determined to belong to the same user. Merging accounts against the will of the user is dangerous and has some significant privacy implications, which is the reason why it is not done anymore and moderators lost the ability to merge users. The easiest way to neutralize all votes and deal with sock puppets is to delete them.

So without any inside information, I'd be pretty sure that this user was determined to be the sock of another user. In this case the socks get deleted outright, and the sock master usually gets suspended. It is not uncommon that if there is one sock, there are more of them, voting on each other. I suspect you just saw one of the socks, and never saw the actual puppet master.

Real users with some positive contributions are not deleted for rule violations in most cases, suspension is usually the harshest punishment that is used. This does not extend to fake accounts that are determined to belong to the same user. Merging accounts against the will of the user is dangerous and has some significant privacy implications, which is the reason why it is not done anymore and moderators lost the ability to merge users. The easiest way to neutralize all votes and deal with sock puppets is to delete them.

So without any inside information, I'd be pretty sure that this user was determined to be the sock of another user. In this case the socks get deleted outright, and the sock master usually gets suspended. It is not uncommon that if there is one sock, there are more of them, voting on each other. I suspect you just saw one of the socks, and never saw the actual puppet master.