Did you watch the video?
You can't say that tail wagging has nothing to do with breeding just because she wags and doesn't breed.
I've had that same thing happen, sometimes even when they wag they don't hook up, it's just a part of the whole process.
You can introduce and introduce and have nothing happen, and just when you least expect it, they do the deed.
I agree some snakes tail wag a bit when striking, but tail wagging during a pairing up is all about breeding and nothing about stress.