My gerbil thumped his hind legs after there was danger?

I know, gerbils thump their hind legs (Mostly males) but about 5 or 10 minutes after danger he thumped his legs on the bottom of the cage, he shares his cage with a female, his sister Lilac, and my male gerbil's name is Dash. Anyway, do you think he did it for mating or danger? I know it's not that big of a deal but I have been waiting for them to mate for a few weeks now, I got them when they were 5 weeks old and they are 12 weeks old now. So I got a little excited when he thumped his legs because that might mean they will mate soon because Lilac might accept the thump sometime soon. Lol. But I just wanted to ask what you thought it meant?