I did a McDonalds shop in south central LA and they were behaving in a similar fashion. Every employee inside the location was Mexican and yelling back and forth in Spanish. My Spanish isn't perfect, but I identified some inappropriate words in the banter. I included some quotes and rough translations in my report.
I returned a month later, and there wasn't any noticeable difference in behavior. Some location's management don't take costumer service as seriously as others. I've especially noticed this in lower income areas.
I did another shop for Ace Hardware in the same neighborhood. I approached an employee, later identified as a manager, and waited for him to make contact with me. He turned around, and with a disgusted look on his face hissed, "What?"
What's deemed "appropriate" varies from culture to culture. Us privileged Americans like to be pampered by people in the "service" industry. We want eye contact, smiles, and people kissing our asses. Mexicans in Mexico, however, just want somebody there to do the job. Take my order, take my money, get me my food, and do whatever you want in between.
Their culture comes to America and sits in communities rich in their population. It is really fair that they get shopped by standards that don't reflect their culture? If 95% of their patrons don't care if they're greeted with a smile and just want someone to take their order, why should somebody like me rush in there and audit them based on my cultural values?