The definition of a gravity knife:
Gravity Knife
A folding or moveable blade knife in which the blade is held in the closed position by a latch mechanism released by a button on the handle or other mechanical triggering device. A gravity knife does not include a knife that can be opened with one hand utilizing manual pressure applied to the blade, or to a thumb stud, declivity or spur of the blade; nor does gravity knife include a knife with a blade that can be opened by means of inertia or other such force produced by hand, wrist, arm or other bodily movement provided the knife has a detent, spring, structure or other such mechanism that provides a
bias or spring-load toward the closed position.
According to this definition in my opinion the DH is not a gravity knife. You need the wrist flick.