It's been two years since I've had chicks. There are two or three chicks right now already at almost 2 weeks old that are jumping up and sorta chest bumping. I remember this from my two previous silkie chicks that were Roos but I don't remember it when they were this little
At two weeks old, it's pecking order behavior. And both cockerels and pullets will do it. Not an indicator of gender at this point.