I just passed a Gen 4 Glock over to my wife. It shoots left for me and her (and she is a lefty). I think Glock pistols have more issues than most with hitting left -- both because of the harder trigger to manipulate straight back and something to do with Glock pistols. Isn't the notch on the Heinie rear Glock sight offset slightly right by design?
Some eyes also work differently. I typically need a slight right correction on the rear sight of ALL my pistols, and a slight left on long guns. Been like that for twenty years. Previously, I needed a slight left correction on handguns and long guns.