One idea is he might have won more than $10k in chips, which meant he would have had to pay taxes. He might have cashed in the $10k (no tax declaration), and then held the additional $3k+ for the next trip.
Also, I've had to show a drivers license and tell the cage what pit I won my $1k chips recently at Mirage. I balked at giving them my license, but they did call the pit supervisor and confirm what table paid them out.

Marc