Gestures are a great form of early communication, and the best thing to do is to keep modeling things like waving, pointing, clapping, etc.
A 10-month old is working on so many things developmentally - so much is "coming together" at that age, so he may have mastered that skill and now have moved onto something else that you haven't even noticed yet! The most important thing is to look at what other things he's doing. Sometimes when little ones acquire new skills, we see other things temporarily disappearing. Overall, though, look at his overall development. If he is starting to use other gestures, if he's babbling, and if he's making eye contact, etc., then that's great!
Also, remember that NONE of us imitate each other every time we see something done. What a boring world that would be! Babies imitate based on what they think is interesting!