unetboot linux mint live drive boots grub2 instead of unetboot

I screwed up big time, I have installed linux mint live disk on my flash drive via unetboot on an virtualised linux mint of another computer. When I transferred the usb drive to my main computer, it DOESN'T show up the unetboot selection screen but instead, always shows grub2 and it's boot options only into my main OS.(which doesn't work at the moment, see my other question ) Before that, I have installed grub2 on the almost everything including the usb drive for some reason via boot repair, I am sure that is what causes this problem, not sure why I did it. It doesn't matter if I format and install the OS on my usb drive, the incorrect grub2 menu always appears. Could someone help me?