If the firmware was flashed wrong, it is more likely that your keyboard is not working at all rather than sending a wrong key event. Since flashing the keyboard firmware manually is more complex and risky compared to flashing and booting a vanilla system image from sd-card, I would try that first if I were you. If you want to flash the keyboard firmware, here is a script that does it and from which you can probably learn all the things that tell you how to do it manually:
script worked perfectly, evtest shows no errors. 100% was the wrong key event.