Congratulations!! Sounds like you are doing better than you expected.
In addition you have found out the really fun part of racing a two-stroke... more people support you than you ever thought possible!!
As for what to tell people when they ask why... we always change what we say, but we aim for funny more than explanations. You can see people's eyes glazed over when you start using logic and reason. But say something funny... their eyes light up, they smile and you made their day....
Answers like... well now when tell my buddies how I went into the corner I go Brappppp! instead of getting them all wet!
Okay that one is kinda lame, but you get the idea.....
When other racers ask us why the two-stroke, we ask why do you need a handi-cap? It's called the 125 class and your racing a 250, why you cheating?
But you can just tell them the truth... because it's so much fun. Fun to beat larger bikes, fun to ride and fun to have so many people come up and introduce themselves.
Enjoy!