Hi Brian,
Brian M:
1) huh? any map for that? haven't had anything like it before or since.
Maybe you hit one of the "psychic powers" in your concentration. I treat the "psychic powers" like any map, i.e. as a description of what leads where, and not as a model of reality. This saves me from obsessing about the (in this context) fairly useless question of "what is real", and focuses on "what is causal", which is much more useful. Have you read the
MCTB Chapter on the Powers? Useful to know. Of course, "psychic powers" is just one model or manner of speaking about these experiences.
2) what to do if something like this happens again? This experience occurred before I read MCTB, so it did not occur to me to try to simply observe the three characteristics in the presence I felt, rather than just trying to ignore it, which did not work so well. Yet, perhaps it is unwise to continue in that sort of situation, or perhaps there are alternative strategies? Any practical advice?
Some suggestions: If you wish to "work" with this kind of experience on the level of engaging with it like it was "real", I'd really recommend cultivating loving kindness, or Metta - send the presence some Metta, and chances are really good it'll "leave". Here's a bit of Thai Forest Tradition advice about dealing with some of the experieces associated with the powers:
Visions & Signs.
Another suggestion on the same level of engagement: in an out-of-body experience, you suddenly have two "bodies" to keep track of - your physical one and your "ethereal" one. The old trick of identifying with the physical body doesn't work any more, so how do you interpret the second body? Say you "identify" with the physical one, then the "ethereal" one may well seem like a sinister presence, and may threateningly rush at you when the experience ends, and the two "bodies" again merge or occupy the same space. So if you wish to follow this track, you might want to read up on OOB stuff and see if it is at all relevant to your experience. (The kinesthetic stuff may be a good marker). Again, as with all powers, I don't worry about whether this stuff is "real", and focus on what is causal, in order to get a skillful view of my experience.
Finally, you yourself mentioned the three characteristics - like any experience, these things can be investigated for the truth. This won't engage the experience in terms of their "content" like the "send metta" and "oob" approaches above. You already know how to do this. Highly recommended

A final remark about the powers: they can be highly fascinating, like most forms of "content" actually. I've had to find a bit of a compromise for myself, indulging my urge to explore and giving it a counterbalance of strong investigation practice. Remember that "cracking the thing", stream entry and so on is also considered one of the "powers" in Buddhism.
I hope there was something useful in there for you.
Cheers,
Florian