Not a useful warning. Wikipedia should include or allow me to access enough information to assess what sort of attack it was. Let me offer three attack scenarios that I could distinguish between. (1) Trivial dictionary attack with nothing but my user name and some frequently used passwords. This would be especially harmless if it was part of a broad attack at many user names. (2) A targeted attack based on one of my actual passwords. This might be a highly personal phishing attack where some other system has been breached and that password is being tested against other systems I might be using. (3) The attack might be based on a breach of Wikipedia itself, where the password they are probing with is a partial match of my actual password. Obviously not a total breach, since that would have avoided any login failure, but perhaps something that allows them to guess highly likely passwords and the failures were incorrect confirmation attempts.
In addition to information about the nature of the login failures, something to help identify a successful breech would be helpful. Right now the only information that comes to mind would be a summary of my edits since the possible attack. I probably can't remember every edit I've made, but I almost surely could recognize weird patterns.
(Why did it MediaWiki apparently log me out? Was that a security thing? Anyway, I don't see any reason not to put my identity on this suggestive feedback (?).)