That paper found the exact opposite of what he's claiming

“Second, we find that subjects who are paired with a partner of a different race or nationality send back less money to their partner. Eleven out of the twelve times in which the recipient sent back nothing, the sender and the recipient were of different races. These effects are stronger than the social network effects and survive controls for the social connection of the sender and recipient. This finding is also unsurprising, but serves as a reminder of the continuing barriers that racial and national differences may create”

and in the abstract:

When individuals are closer socially, both trust and trustworthiness rise. Trustworthiness declines when partners are of different races or nationalities.

You can't make this shit up