The problem with this link might be a user error: https://en.wikipedia.org/w/index.php?diff=prev&oldid=644543349
The simplest way to do this would be to accidentally paste the link a couple of times, without blanking the link field first. However, I'm posting it just in case it turns out to be a wider problem, and also to point out that if the link box were wider, this would be less likely to happen.
I have seen this anecdotally a few times, but only in the context of VisualEditor removing this kind of stuff.
I found this because the removal was tagged, but the creation of the
problem was back a few revisions in the edit history.
The title as written is wrong. "Linkhttps://en.wikipedia.org/wiki/Link" is a totally valid name for a page – see http://en.wikipedia.beta.wmflabs.org/wiki/User:Jdforrester_(WMF)/Linkhttps://en.wikipedia.org/wiki/Link which I created to demonstrate this.
Can you think of a more specific ask? "If the user has written 'https://' in their link target but not at the start, suggest they might want to make an external link instead"?
Since there's no difference in how VisualEditor makes internal and external
links, suggesting that the user make an external link is going to be
confusing. How about a warning that says "Please review your link target
to make sure that <display mess here> is correct"?