Yes, I assume they crawl or have crawled the publicly accessible internet. Who knows if they honor robots.txt or not. And who knows what IPs their crawlers use. The cat's out of the bag.

I didn't mean to single you guys out. I just noticed a few from your site and mentioned it. I'm sure if I would have scrolled more, I would have found more Nostr image hosts. 
 

 Good observation, I didn’t know what you were talking about until I searched your image. There are a LOT of links from nostr.build.. I also think there is not much anyone can do about it overall, but we’ll block what we can..