I'm sorry, but you actually misquoted him here. It says:
"If an attack of opportunity is provoked, immediately resolve the attack of opportunity, then continue with the NEXT character’s turn..."
Emphasis on NEXT character's turn. Not the current character's turn who you just tried to trip. Now obviously it wouldn't be fair to the person who you just interrupted to just skip over their turn (unless of course your AoO completely nullified the rest of their turn), so if you continue to read it says:
"(or complete the current turn, if the attack of opportunity was provoked in the midst of a character’s turn)."
It was provoked in the midst of their turn, so we will complete that character's current turn... and assuming the trip was successful, that makes him fall back down. So he just expended his action to get up and can not do it again this turn.