Average male weight in Germany: 181.7lbs
Average male weight in USA: 190.9lbs
So basically the difference is roughly 9lbs, so yes it is quite possible that those 9lbs may be due to different consumption habits but 9lbs is tiny compared to the hundreds of pounds of differences between thin and fat within populations.
How much slimmer are you than your parents/grandparents? If they have BMIs in the 40s or 50s I will be impressed but it's still anecdotal.In my family, we take extra weight very easily. Yet my body mass index is within the "normal range" (23, a number that would make me rather slim compared to the US standards). It's a choice: it's because I know what I eat and how. You have to educate your taste buds since childhood.
I still stand by the fact that you can't eat yourself very fat unless you have the genes to do so. Overfeeding to that extent isn't easy it's actually very difficult you'd need to constantly gorge yourself past desire. It would be very hard work and your metabolism would be going into overdrive you literally wouldn't be able to stand still. There are plenty of overfeeding studies around on google scholar.