Why does the list contain so many sub domains? Wouldn't it follow from facebook.com being meta owned that weird.subdomain.facebook.com is also meta owned?
Exactly, that is what I meant. The OP seemingly uses IP whois to identify meta (it is from a mastodon blocker). The condensed list removes subdomains to make it worse.
Full enumeration is useful for security research. For blocking purposes it can sometimes be helpful to enumerate it.
And on your question: it is most often the case that a subdomain is owned by the same entity, but it is not a given.
The most common thing is a CNAME to some site of a vendor. But you can go all the way to full subdomain delegation (this is the same as going from com. to facebook.com.).
