tried to use unetbootin as a sanity check, to start with it seems to not even bother erasing/formatting the USB drive? After burning the freedos ISO on a flash drive using unetbootin, I looked at the drive and old files from before burning were still there. Then after that, indeed while booting it pops up a boot menu (that shouldn't be there) that needs modification. After some searching it seems their bug tracker has a a lot of reports about this, they're not actually writing ISO images as is, seems they're overwriting any present isolinux with their own version or something. 0/10 do not recommend