It's called being sensible. Like... We all take risks when we go out, but it's like wearing a seatbelt. Does it eliminate risk? No. Does it reduce risk and is low risk in of itself by wearing it? Of course.
And ultimately, the insensible thing is banning masks.
If I'm in transit on airplanes and in airports for 8 hours and I wear a mask for 7 of those hours, the one hour (or probably less) that I take off my mask to eat a meal doesn't completely negate the good that wearing a mask does for the rest of the time. I'm still reducing my risk (or the risk I pose to others around me) for 88% of my travel time.
There's a huge difference between sitting at a table by yourself (or even with a family member) and, say, sitting next to a stranger in an airplane. Walking through the restaurant and keeping the mask on so as not to catch or give anything in passing is sensible. Greater distance means lower risk.
But he's about to sit down near those people and take his mask off in like 45 seconds. Then he'll sit there with his mask off and everyone else in there with masks off for 30 minutes at least. That extra 45 seconds is not really helping anything.