When your neck and shoulders feel tight, this technique focuses on the hand instead of directly working on the painful area. By raising the thumb and gently bending it with the opposite hand, the movement may create a stretch through tissues and nerve pathways connected to the upper limb.
The idea is that changing tension in the forearm and hand may influence how tight or relaxed the surrounding muscles feel, including the trapezius. However, the claim that this will immediately resolve trapezius stiffness because the nerves are "connected" is an oversimplification, and results can vary from person to person.
If neck or shoulder pain is severe, persistent, or associated with numbness, weakness, or other concerning symptoms, it's best to get medical advice.