Clearly they weren't actually playing Bingo, and instead were bidding for Chris. I could tell holding up a Bingo card indicated they were bidding, and the whole notion of using Bingo was a jab at white culture in the US, but what I don't understand is how the bidding worked.
It was evidently some kind of silent auction with the father holding up different numbers of fingers, but I don't know if this was meant to indicate dollar amounts, or bidding rounds, or something else? If they were dollar amounts, are we talking thousands or millions? Or is this something we're not meant to actually understand and just infer?