Is he happy all day, not cranky, and "engaged" when he is playing or learning? Then don't worry about it! There is no "perfect" amount of time to sleep at night!
he is getting 11 hours of sleep - that is almost half a days worth... it sounds like plenty to me. The "time" doesn't matter near as much as the quality.
My daughter has a different sleep schedule at 2 then most other kids. she goes to bed at about 11:00- 12:00 pm with my husband and I, and she wakes up usually around 9:00- 10:00. Because I am a SAHM- we don't use alarms... so she wakes up when she is ready to wake up- her own natural timing.
Some days, she takes a nap. Some days, she doesn't. She knows what a nap is, and she'll ask for one if she is tired! When she is awake she is alert, engaged, happy, learning etc... THAT is how you judge if your child is getting enough sleep- not by the clock!
Who cares what the other preschool kids are doing? (I mean... they SHOULD all be doing whatever is best for them- and their families) What is "normal" is not always "right" or "best"- and shouldn't determine how you make these decisions. Instead judge based on your child alone, and what keeps him happiest and healthiest (which usually go hand in hand).
Good luck!
-M.