Siegs B6 is godlike in this match up. Didn't see enough of it and Aga (JF or not) is just something you don't use against Roth but I digress. It was a good fight.
Seeing the replay is making me wonder how. Then again a lot of the stages in SCV seem to glitch where walls meets edges. So I'm assuming it's a combination of situation and Siegfried being weird.