My four year old son has preferences (who doesn't).
To me it sounds like your ds is more ritualistic and obsessive than a typical 4yo, but I can't tell whether it's to a worrisome level (the fact that he can "get over it" quickly is a good thing). You can ask his pediatrician about it. Write down as many examples of ds behaviors/obsessions as you can to give the pediatrician, and ask whether the behaviors warrant further investigation and testing. IF there's a problem, it's always best to address the problems earlier than later.
My son is in a ritualistic phase right now as well.