You see the helo coming from the left on the screen while the airliner appears to be descending. The helo must have gotten in the way (as opposed to catching up from behind). The airliner's lights are unmistakable, so how did the helo pilot not notice them? The airliner's pilots might not have had a chance to notice the helo. Since the helo was crossing an active runway approach the fault has to be with them.