Well it might be Roddenberry’s half remembered recollection of his friend’s middle name.
"Might" is a word that, ironically, has no power. It's meaningless without hard data, and we have none.
One source on Google claims that Noonien is a Chinese name meaning "gifted one," but I can't find any support for that in online Chinese dictionaries; the Mandarin word for "gifted" is tiāncái. The closest thing phonetically I can find is niúnián, which means the Year of the Ox.
As for Sikh names, I tried looking up male names starting with N, and the closest things I could find were compounds beginning with "Noor" (divine light), like Noorinder or Noordev.
Anyway, sources disagree on whether Roddenberry's friend was named Kim Noonien Singh or Noonien Wang, though the latter seems more likely to me, since "Kim" and "Singh" in the same name is an improbable mix. All we have is a muddled account based on Roddenberry's own uncertain memory.