[gvb]

It is probably fully deflected. If it were deflected inadvertently, it would be very difficult to recover control of airplane pitch at the speeds and low altitudes where this occurred.

Another possibility is that the elevator control itself was lost and the pilot is desperately attempting to regain control using the trim tab to control airplane pitch.

[ktsmith]

There's a new picture of the plane (though I can't find it not embedded in video) showing the tab detaching. In the best picture I've seen the tab is perpendicular to the tail and then in the next frame is completely gone.