So this begs the mildly racist question, do Japanese people fart? Can they light their farts on fire? Maybe not if the seaweed in the diet kills off methane producing bacteria.
https://www.cooksillustrated.com/how_tos/6385-flavoring-drie...
Some stereotypes are based on loud minorities, but others manifest due to the it being true on a statistically meaningful scale. I think it is safe to say on average Japanese have more seaweed in their diet. So if I met a random Japanese person and assume they eat seaweed, then I am stereotyping, but it is rational and informed stereotyping, nothing rude about it.