I think it's a throat latch which is attached to the under collar when not in use? Similar to the throat latch on a classic Trenchcoat.
It sur is, i just don't understand the design of it...
Why does it have buttons and velcro?
Ohh, maybe there is a patch of velcro in the back of the neck similar to the one on the collar. And the button is there to fully remove the latch if not needed?