Possibly a combination of two effects:
1) You only drew Shredder. Even with a 500 rating point deficit, one can get a "lucky" draw.
2) For any stated handicap rating, I've found Shredder to be weaker than most other engines. (Well, I have Shredder 12 - I don't know how Shredder 13 performs.)
I just drew shredder on 2200 I only have 1700 USCF rating. I know I'm getting better but I know I'm not near master level. I have shredder on random openings so he started with G5 after my E4 and I was able to hold on. Anyone care to enlighten me on how shredder behaves?