Is a critical required for the Great Weapon Master extra attack?

@JeremyECrawfordGreat Weapon Fighting requires a critical to trigger the extra attack regardless if a creature falls below 0HP, correct? Sorry, I meant Great Weapon Master. Is a critical required for the extra attack? it's the "with one" that is confusing us.

— Kenn Durrence (@lockedgrooves) February 23, 2016

Great Weapon Master grants its bonus action if you score a crit or drop a creature to 0 hp with a melee weapon. #DnD https://t.co/5sxIvLx16n

— Jeremy Crawford (@JeremyECrawford) February 23, 2016