Let me re-phrase your question: "why did I post this thread?" that's one of the problems.

The general problem is using something for an unintended purpose. In some cases this may be OK, until it's not OK anymore.

/etc/hosts is used for resolving network names into IP addresses (like a local DNS cache), not for ad blocking.

So the general thinking goes "if a assign an invalid/local address to an advertising server no connection will ever be made to it", disregarding that "if I want to find the name of a given IP address I will get ambiguous, invalid, results."

You've been hit by the latter in trying to achieve the former.

Note that a server bound to 0.0.0.0 as a listening address means that the server accepts connection on any address, normally meaning from any interface (as opposed to, say, only from localhost, only from WAN address, etc.)

So whenever a networking tool wants to show a nice name for 0.0.0.0 (it should not, but it may try) then you get that doubleclick.