Can a driver be arrested for broken tail light?

My father-in-law (who is Hispanic) was stopped by law enforcement for a tail light that was not working on his vehicle. His vehicle has plates, and he has a driver license from another state. However, instead of issuing a citation, the officer placed him under arrest. There were no other violations, nor did he have any outstanding warrants. Luckily, his wife was in the vehicle (with four of their grandchildren who watched the whole thing), and was able to follow the squad car to the station, where they promptly had to pay a $350 fine. Once they paid the $350 fine, they released him. Isn't this discriminatory or am I missing something?