Handedness stereotypes are not "proof". Like the majority of left-handed people, I wear a watch on my left arm and zip up my pants with my right hand. We live in a right-handed world and thus have to adapt.

Before electronic watches were common, mechanical watches were wound with a stem at the 3:00 position. They were always on the left wrist so you could reach the stem.

I'm right handed and have always worn my watch on that hand. And regardless of handedness, the fly on a pair of men's pants is always on the right hand side so it's going to be easier for anyone to zip it right handed.

More likely, the whole thing was a set-up and four separate tips were left with different members of the force to get them all out of the way for the evening and create doubt within the system.