I would think celibacy is the opposite of promiscuity. Poly is on the same half of the romantic/sexual monogamy/non-monogamy 2-dimensional spectrum.
Article was tldr, but I have spoken with enough millenials to get the general impression that they're less and less interested in the idealized monogamy portrayed in subculture, and more and more interested in doing their own thing.
That being said, Auto's daughter was raised around poly and she's decidedly very monogamous. She doesn't like to share, and she doesn't even have multiple crushes concurrently, let alone relationships. So it's by no means a "monogamy is dying" type thing. More that the new generation is just better at exploring and telling pop culture to go fuck itself.