Sometimes, it might just be the individual concerned is in deep thought about something and isn’t ready to talk about it and/or just wants to enjoy the meal in silence due to something happening earlier.
Not everyone is willing to share something at all times and forcing the issue tends to be counterproductive(makes them less inclined to share/confide later).
As one who was the same to his parents, he’s possibly doing it out of a combination of attempting to alleviate any possible worries by not bringing them up with you along with asserting his own independence…including handling issues himself without parental involvement/input.
It’s doubly so with some similar-minded friends who have parents who react badly to bad news(i.e. temper tantrums, crying jags, etc).