I'm stuck right now... my parser is suddenly getting this popup. Is it legit?

That url is in the signature of https://bitcointalk.org/index.php?action=profile;u=9428

Would your crawler try and follow that link for any reason?

No, my crawler does nothing but load the page - does not follow or index any links.

I have noticed there are some old profiles that still have an avatar from an external source, and they time out when I try to connect. Examples:
https://bitcointalk.org/index.php?action=profile;u=3758
https://bitcointalk.org/index.php?action=profile;u=5153

I feel this is somehow related to that issue.