Elon said it, let's put it to the test.

I don't know what "self-growing" means here or even "city" but let's give the lunars the benefit of the doubt and say "we'll know it when we see it."

• Wikipedia gives us "permanent and densely populated place with administratively defined boundaries whose members work primarily on non-agricultural tasks" for city. And although no hard number is given, it's more like tens of thousands than like dozens.

• "Self-growing" probably means physical rather than population expansion? So we should look for an increase in physical size principally from raw materials from the Moon itself. On the other hand Musk is a population growth enthusiast, so possibly he meant that, so in the unlikely event that on-Moon human reproduction exceeds the death rate, maybe we allow that as well, if the statistical sample size is large enough.

Suggestions welcome from the comments.

This resolution is potentially subjective, so I will not trade on this market.