I have no idea. It's an Onomatopoeia word: one that sounds much like what it describes. (if you already knew that sorry for the explanation.
No doubt they're using a thesaurus and relying only on that. Nope, I take that back. I just put the word "howl" into the manuscript I'm typing and hit the thesaurus and then went down the rabbit hole of other words and "keen" never came up.
I can't imagine using that in a steaming love seen. I just sent the info on to another friend who writes some pretty steamy stuff, can't wait to see what she says. I mean, not even in (mummble mumble letters letters) type of leathery stuff would that be appropriate.