I feel like that's selection bias at work. When you're traveling, by definition you aren't going to see or interact with the people who aren't there, who might be at home, feeling lonely.

And I'm not sure interacting with customers as someone who works in a coffee shop or a food stall is really a sign either way. Many (most?) of those relationships are surface-level at best, and while some people might get to know the person who makes their coffee on a more personal level, and actually see them outside of the context of their job, you can't really tell that just by what you see as a traveler.

I'm not saying these workers don't derive satisfaction from any of this, or that it's not meaningful interaction, but these people could still be lonely in their personal lives.