It never happened. Very clearly, AJ shoved Glazier's head down unnecessarily after the match. Glazier stood up and gave Ferrari a shove back. Then AJ threw a slap and flipped off Glazier.
AJ is using Chael Sonnen's satirical explanation of what happened as a legitimate defense and justification for his actions. Notice he didn't apologize to Glazier. Could've said something like "both of us made a mistake" even if he truly thought Glazier was at fault.