Maybe because a lot of people who sell KOs mark them as "Asian reissue" etc., so some people may associate any toys that are perceived as exclusively Asian or Chinese as being fake -- so perhaps the seller wanted to assure that while these toys are Asian exclusives, they are legit.

That's the stupid thing about people referring to KOs as "Asian" or "Chinese" because not everything from the Asian/Chinese market is fake. Even the term "Asian/Chinese reissue" can be a misnomer because there are legitimate Chinese reissues of G1 toys approved by Hasbro. Just call a spade a spade -- if a toy's a counterfeit, just say that it is.