You're close! It's the little multi-tool that was furnished with the FWB 65 match pistol. The long end fits the trigger location screw, front sight element clamp screw, etc. The short prong is for the trigger-weight tumbler under the front of the receiver.
Here's one with the pistol (and the similar tool that came with the FWB 300S rifle).
Excellent! It appears that the same tool was used on the 65's successors, the models 80 and 90 (even though those models dispensed with the two-mode trigger).
This image is a model 90, from Danny Garvin's superb "Vintage Airguns Gallery" site: