[ChrisV]

The message of the overraise is that SB doesn't want a fight. However, if you pick one with him, I think he's going to call. With a mediocre hand I think he would have folded.

The thing to remember is that a lot of your opponents only decide one thing at once and don't look ahead. Even though logic dictates that if you intend to call a reraise but don't want one then pushing is the way to go, people routinely raise without really thinking about what they will do when reraised.