Ok, just try this..........
Assuming it takes at least about 30 secs or so to "FLSH" the image, as soon as it goes to reboot remove the USB stick and see what happens.
Any less than 30 secs or so, I'm working from memory remember, so don't quote me on this, then a full image has not been flashed.
Remember it is practically impossible to fully "brick" these boxes from using a USB device to flash, unless a wrong bootloader has been employed. Hence my advice to never even attempt to flash it, as it, in the normal course of events, does not require it.
If your box is displaying "Boot" and then "FLSH" it is NOT bricked.