I was hoping https://mybrandnewlogo.com/how-it-works was a little more in depth of how it actually works but I suppose if they gave away their secret they wouldn't make any money :)

I'm guessing they have a stock library of vector art somewhere. I'd love to know what library / libraries they have used.

Edit / added:

On a different topic. I routinely by logos from Fiverr for about slightly more than these (typically $80 - $100) and generally speaking the one's from fiver weren't using any stock art.