Bill says he never heard hammering during the construction of the McMansion, yet the construction scenes showed lots of workers hammering. Also, the first morning shows Hank, Peggy, and Bill disturbed from their sleep by construction sounds, which distinctly and clearly includes hammering.
When Dottie's nephew Eric rolls up and finds the guys drinking beer in the alley, he mistakes them for Mexican day-labourers who don't or barely speak English, yet Hank, Dale, Bill, and Boomhauer are exceedingly and clearly white people. This is an impossible mistake to make, even for the most shallow, oblivious person.