I'm not saying that waitressing doesn't involve interacting with other people. In that sense, it's social. In a past life, I was a busboy, and while I didn't have to talk to customers nearly as much as the waitresses, it still wasn't the same thing as, say, being at school, around other students, or making small talk with casual acquaintances. I mean, you can't always talk to a customer the same way you'd talk with a friend or peer outside of work.
The point I was trying to make is that it's a different type of interaction than, say, if you were going to party where you might not know everyone. In the one case, it's your job, so that if someone says something offensive or treats you badly, you pretty much have to grin and bear it, where in the other case, you're more free to disagree, or to just tell them flat out what you think. Both of these are "social" in the sense that you have to interact with strangers, but, to me anyway, they seem like different kinds of interactions.