Most open source keyboards have a button you press to switch from KB mode to flash target mode. Not sure how this laptop works but a solution would be to require the user to hold fn and some other key for a few seconds before it will accept firmware.

This problem btw is actually present in a lot of devices you already use but it’s proprietary. People have found out ways to flash firmware to USB devices, SD cards and hard drives before. It just requires reverse engineering to work it out.