Note the thick chord of the Elevator vs the Stabilizer. My guess they were looking for greater strength via the thickness as well as maybe getting the airflow not to separate and as stay laminar as it went over the gap, by causing it to accelerate. More effective elevator for a given span is my guess. I have seen this technique used on one Acrobatic Aircraft's Ailerons...
“Is this post the trim tab separation?”
No. This pic I just found and shows some buckling of fuselage. Classic damage caused by overstress.