Sounds to me like someone had a disappointing experience at a GM dealership.
I’ve been a service manager at an independent auto repair shop and at an electronics repair shop. Generally, the best techs (at either job) didn’t have the best people skills. Their interest and focus at work was making ‘things’ work, not developing positive business relationships with customers. That’s one reason dealerships have service writers who are the interface between mechanics and customers. A lot of dealership mechanics work flat rate, so if they’re not turning a wrench (like when they have to talk to a customer), they’re not making any money.
When pulled off a job to talk to a customer, I’ve seen techs be surly, rude, unfriendly, and obviously more anxious to get back to their work than making nice with the customer. Not all mechanics are like that, but the techs who excel at their craft, and have excellent people skills too, are few and far between.
Just a guess.