If I had to guess, I don’t think the firmware was properly downloaded. GitHub doesn’t make this really straight forward, but try using this link instead:
Extract that and see how the file size compares to the one you tried. I suspect it’s bigger?… Then just repeat the flashing process with the file I provided and see how it goes.
P.S. By the way, you don’t ever need to plug the Wi-Fi Adapter into USB. That’s just to give it power, which the Game Frame also does.