It was a 5c; 5s and later had the SEP. You don't 'flash' a fake ios; you can use the bootrom exploit to put your modified version of ios into memory, and once

It was a 5c; 5s and later had the SEP. You don't 'flash' a fake ios; you can use the bootrom exploit to put your modified version of ios into memory, and once you reboot you would get back straight stock ios. They could even make it reboot as soon as the password was harvested, leaving behind no trace. This is scary stuff. You can keep yourself safe by rebooting as soon as you get your phone back from border patrol, but many people would not know to do that.