To say "thrust" (or, if you prefer, a force in the forward direction, if "thrust" is somehow associated with engines) is correct. The winglet doesn't just, if designed correctly, "reduce drag". In a manner similar to the sail on a yacht while tacking, the careful correspondence of the winglet angle and the direction of flow of the local tip vortex flow is such that the "lift" generated by the airfoil that is the winglet is - very slightly - oriented in the forward direction. Thus there is indeed a forward force component.
No, there would be no force if there were not air flowing and a vortex - but that applies to any airfoil in any orientation. We do not say that the engines produce "lift", even though the answer to "Would [those winglets]
the wing be producing any force if the engines weren't propelling the aircraft through the air?" is also "no". So why deny that the force generated by the winglet acts forwards?
(And yes, even with the induced drag accompanying the winglet lift accounted for, the force vector is still forwards, at the winglet design conditions. Off-design, it's a different matter, which is why winglets are so sensitive to the mission and design point of the aircraft.)
Oh and to save a lot of typing ....
we've been here before 