I suspect that somebody in the company wanted to have an excuse to fire the driver, and knew just that would set him off.
Those libs posting at the article, complaining "he violated his contract" would probably sing a different tune if it were a case of a gay driver being told to drive a sound truck for the Westboro Baptist Church, or a feminist being told to drive a pro-life sign truck.
Thanks for the extra information. I agree with you that it sounds like a set up. In any case, it’s not a breach of contract, although the company making the “donation” is entitled to fire the driver for this reason (or in my opinion without reason).