Like the others have said, he rode faster. It is hard to tell why he out paced your this time. Sounds like he has had more training in the last 2 months, he could have tapered better and peaked for the race, you might have been tired or not quite right nutrition wise.... So did you beat him in the end? Was your overall time faster? Did he light up the bike and have a slower run?

I did a local sprint Tri earlier this season on my Tri bike converted to a fixie rolling on Velocity Deep-V 32 spoke rear and 28 spoke front. Averaged 24mph on that course with a decent little climb in the middle of it. Don't count on aero wheels making that much of difference in shorter races, the engine matters much.