Its because, if you have Ah2h, then Th9h will give you a better two pair than his (counterfeit),
and a flush. If you have As2s however, then Ts4s will only give you a flush. So with As2s you have just as many ways to make a flush, but you have one more way to win on a counterfeit. This is admittedly very nerdy and took me a while to figure out