I don't think you ought to micromanage his relationship with her, but you could state your opinion to him.
I do think it is pretty weird he doesn't communicate with her to make sure they both agree and are on the same page in terms of what kind of relationship they share here -- a soft swing thing or a polyamory thing or what.
For my own definition? "Polyamory" is the capacity/desire to love more than one at a time.
"Polysexual" to me is the capcity/desire to have more than one lover at a time. (not necessarily group sex with them, but have more than one lover.)
One could be polamorous, polysexual, polyamorous AND polysexual, or neither.