well, I'm not sure whether to disappoint /a/, or not.
Fact is, they're right, and wrong.
They're basing their tl on the song(which is from, as many of you faggots know, a international Chinese restaurant chain), which IS in essence what the translation says. Nyan is just the Japanese romanji for the letter that's being used. The letter (which in Japanese would be Musume) IS indeed pronounced Niang in China.
Of course, I'm ignoring the second line, none of my business.