You should of course be cautious about assuming a cursory look from a 3rd party is enough to know for certain how the device is bricked, but it's not abnormal or weird for a business like Sonos to use a half-baked technical strategy to brick their devices, and then to just stonewall anyone who calls into support.
Half of the time that a company says, "there's no way for us to do X", what they really mean is, "please go away now."