I get the sentiment you're going for and it seems very popular to shit on parents but as a dad myself with quite demanding kids I'd be more .. hesitant to make judgments like that. There literally are a million reasons I could behave like that. I could have just spend an entire week with them, ceaselessly catering to their every whim. You know this won't ever be enough. They'll yell at you all day any day to look at whatever they're doing if you're not putting in some boundaries.
I imagine this guy just told them a minute ago he needed some time off and what do you know, the next second they come and claim attention, and he is now stewing in his righteous anger-silence. You also don't know what's going on relationship-wise. In general I'd say mind your own business.
Same thing with the childless people complaining about kids having tablets in restaurants. Well, let me know, so next time I'll place two tired and severely hyperactive kids right next to you so you can enjoy their endless whining while I'll sit a few seats away shoving down some wine thank you very much.