Apparently yes. They only started posting these signs because of foreigners. As far as I can tell, Japanese people are more like American people in the 1980s when I grew up. Back then, food allergies were extremely rare. Even among my age group, they seem to be very rare, but I saw it a lot among younger people while I was still in the states. Airplanes used to give out honey roasted peanuts, if you're not old enough to remember, and they were fantastic. But then sometime in the 2000s I think, they stopped because so many people suddenly had deathly peanut allergies. And it's only gotten worse.

I'm not sure why Americans have so many food allergies these days, but I can only guess it something to do with either food quality, or parents that don't make their kids eat various foods. Japan has long had a culture of eating whatever food your parents gave you, and absolutely never wasting food.

As for dietary restrictions, yes, that's absolutely a thing unique to foreigners here. Japanese people don't have silly religious restrictions about food like other cultures, and vegetarianism and veganism are not terribly popular, though they are slowly growing.