Imo, and just my opinion, they had already made there mind up too deny him entry. Maybe for the back to back entry's (If he indeed has a lot, he hasn't said) maybe for suspicion of working etc. Fact is, when they start down this route with people, they are already in a frame of mind to deny the entry, imo.
I've stated enough times, if they ask, its 99.99% of the time, asking for 20,000 baht. The only rule worth considering is the rule they make up on entry points.