Yuck! I am so sorry. Honestly, given that he only got sick once, I don't think it does sound like Noro. Having 2 boys of my own and working as a Preschool teacher (of 3 year olds) I can honestly say that when they get it there are usually multiple rounds and days of not eating well. Not that it helps, I know, but I think you can breathe a sigh of relief if he's back to himself today!