Not your fault, but this is getting more confusing. You have outlined what you know from different sources, but I know this from Indian sources
Kalonji, black cumin and nutmeg mean different things and I am unable to come to a conclusion on this. Kalonji is the closest in shape (triangular) with a strong smell, but kalonji is definitely black onion seed. There are so many contradictions in the link you provided, like this one
"Kalonji refers to the small black seeds of the Love-in-a-Mist plant. Sometimes they are confused with "onion" seeds or black cumin or caraway. The seeds are deep black and sharp-cornered."
Hindi and Urdu = Kalonji Indian = Nutmeg flower
Sorry, but looks like I may have to go with the sources you provided for getting black seed. Would have been a lot easier for me to get it from Indian stores if only I knew what to get.