Must feel great.

Seriously, can anybody explain to me what this nickname is? Is it a kind of dummy user for anonymous posters?

First, let me answer the actual question: there are plenty of 'unknown (google)' also 'unknown (yahoo)' on MO. This is the name one gets if one logs in with an OpenID from the respective provider and does nothing else (relative to the user profile). Of course the different ones are separate users, and just the display names match; but matching display names are never excluded, and exist. Most of them with very low reputation, one time log-ins or somesuch, but also some with reasonable high reputation. The one in question 3k, but there are a couple others around 1k. [One person apparently even made a play on this, or so I assume, and goes by unknowngoogle, without the space and parenthesis, around 4.5k]

Second, the specific unknown (google) in question is me (ok, this means little too); but just to document this is not an abstract contribution.

Third, there are various anon/pseudonomys users that regularly vote. I do not see any actual difference. What I mean, I can understand that it can make a psychological difference (in the sense your 'must feel great' suggests) to be able to link the user to an actual person, but wheter unknown (google) or any of not too few pseudonyms vote, and they do vote, I don't see it. Or, also those people that seem to go by their initials without further information in the user profile [for some I believe to know who they are, but not for all].

Fourth, however I can understand it is perhaps inconvenient if I vote with an unspecific name on main, and my meta and main name don't match. As also documented by second point I had to write because of this. So, I promise I will get a pseudonym on main and a matching meta user name. Also, as I hope is documented by my first point, the name is not specifically chosen to be somehow rude, but merely an unchanged default, which I left initially for laziness and then later for reasons I will explain, in case anybody asks.

Finally, in case this is also part of the question, is the vote to close on this question somehow unusual or the justification rude? (This is meant as an honest question.) My rational was: Career advice questions get closed frequently, and various people here argue there should be none at all (personally I find this a bit too strict). Yet, this specific one seemed particularly far removed from the purpose of the site. It has nothing to do with research or mathematics, even with or. It is for teaching letters for a teaching job (nothing against teaching, but it is not research) and I doubt that the situation would be much different if asked for several other subjects, so it is not even on mathematics specifically. So, I really can't see how this is on-topic; to me this is further outside the scope of the site than most other career questions, some of which I even answered, that have at least something directly to do with mathematics (as opposed to just being asked by a mathematician). I left the comment, as I thought it was generally considered as good form that at least the first person to vote to close leaves a comment with an explanation. And, gave this explanation in a compressed/less specifc form.

I believe this user used to be unknown (google).

@an_mo_user: I am looking forward to your new pseudonym on main.