Thanks everyone for your replies! I talked to the mom online this morning and he didn't have a reaction last night. I'm going to be more careful in the future.
My son has only bit one other time that I know of, and that was at his old daycare about a year ago when another boy wasn't letting him on the play structure. We're working on other ways to deal with anger and frustration and if he bites again he knows there will be serious consequences!
Thanks again.