At higher levels of chess, it is futile to play games. The players know the position and where the pieces should be. At lower levels, there can be cheating or uncaught mistakes at speed chess and sometimes ridiculous positions develop, such as a player having 2 bishops on the same colored square. Any illegal move that is caught by the other player, while on their own time, results in a loss for the offender. Often there are on-lookers who are watching and have been known to comment when something is not right.
I can imagine but these guys were not hustlers as they were playing out in the open with many eyes watching and they were registered with the USCF, so no need to hustle, at least the guys I am referring to in Dupont Cirlce and definitely NOT the Black GM I saw a few times. In this case no tricks, just straight up chess, many games were set at 5:5 minutes.