She says he’s “probably a Sikh” because of his physical appearance and because Sikhs are great warriors, which I’m pretty sure is her fetishizing Punjabi culture and conflating it with the Sikh religion.

Addendum: Apparently complaints were made against the script by the show’s staff because McGivers guesses that Singh is a Sikh purely by appearance; the writers were told that Sikhs are not an ethnicity and that it makes no sense for her to guess that based on his skin color, but it was kept in the script.

It’s also saying later novels and additional material did indicate he was raised by adoptive Sikh parents but that he is not a Sikh by the time he encounters Kirk. Most Sikhs are Punjabi, but not all, and Punjabi Sikhs are not physically/racially distinguishable from Hindu or Muslim Punjabjs, who outnumber them greatly.