This is what I call a "fake spray". Cats will back up to surfaces and "spray" urine on them and their tail will quiver at the base vigorously while doing this. They do this to mark territory.
My cats have never actually "sprayed" urine, but go through the motions, mostly when they are happy or expecting something like treats or food or playtime. I've always just called it "fake spraying" I've had male and female cats both that did it. I've never seen either of my current cats do it. I think its just a kitty idiosyncrasy.