You are aware that there are millions of Japanese and Korean Americans who would care about this issue, right?
At 1.3Million, sure, it's possible, but I don't personally think there are enough right-wing revisionist history Japanese-Americans to have generated this much response.
Anyway, the facts support my assumption directly from the petititon. The vast majority of Japanese names on the petition do not list their location, while a handful directly report they are from Japan: Taizo H - Tokyo, Kuniko N - Fukuoka.
More importantly, the site is utterly impotent. It's not like voting or campaign donations by foreign nationals, so I'm not sure why it matters. If some Japanese wingnuts want to embarrass themselves on the site, more power to them.