To be fair, the bit about Khan "possibly" being a Sikh was mentioned once
in "Space Seed," forty-six years ago. It wasn't mentioned at all in The Wrath of Khan.
Granted, I got two books out of that line, but I'm inclined to cut them some slack here. Khan's Sikh roots are not essential to the character; heck, Khan never
mentions them onscreen. He identifies as a genetically-engineered superman, not a Sikh.
The way I see it, one line of dialogue from forty-six years ago is no big deal. As the saying goes, sometimes an ounce of inaccuracy saves a ton of explanation.
Or, even more profoundly, why sweat the small stuff?