To maybe go into some more detail as well, I do feel like the general culture of dinner in northern Germany (and Scandinavia, apparently/perhaps) is that it's "private time". As in, family privacy. So, as a kid, you didn't want to impose on their family time.
Like, this classic very hospitable American dinner where the father casually talks to his son's friend about how he's doing and stuff... is simply not how it was for me. That kind of thing for some snack in the afternoon, sure, not uncommon. But for dinner time? No.
Furthermore, and that does apply to my case quite a bit I'd say, it's not just that you'd want to upset the other family for feeding the kid that's then no longer hungry when at home and eating their own dinner, it's that you wouldn't want to upset the other parents by feeding their kid food which they aren't happy with. Since my mom was extremely against junk food, sodas, and often even just non-whole-grain foods, she wouldn't have taken kindly if I were given such a meal. Like, in hindsight, it would've even surprise me if my mom maybe had the one or other talk specifically telling those other parents that she wouldn't want me to eat that stuff/eat there in general.
There certainly wasn't as much general respect for other families' cuisine, which does appear to be the case for many cultures. Again, something like declining an invitation to stay for dinner is/was entirely common here.
Funnily enough, my aunt from my mother's side of the family is someone who has taken some of this to the extreme, though. Their family legitimately eats fairly unhealthy (Cola, much fattier, no care for whole-grain, etc. pp.) but generally also just doesn't share anything in common that my mom or us kids liked to cook. So uh, even recently when she visited my mom a few days after her birthday, they still brought some fried chicken and stuff to heat up, lmao. I also was once in the position where I made a lovely chili con carne (I dare claim) with some white or brown basmati rice on the side, and the respective uncle got upset for me having added some rice to the plate already. He later added some ketchup, too :|
Now, that by all means is pretty rude. Though I suppose, even there we roll our eyes and shrug it off. It's silly but hardly a capital offense.
