That video pre-dates the HTC method. Also, in order to flash a RUU, you need to lock the device, first. I don't recall if flashing a RUU will revert it from Re-Locked to simply Locked, but I don't think it does.
And that RUU listed in the guide you linked is an older Sprint one. It won't flash on a 1.5x HBOOT, as you have to flash the same revision or a higher one unless you're S-OFF.