From the Apple support page
If you changed the date to May 1970 or earlier and can’t restart your iPhone, iPad, or iPod touch
Manually changing the date to May 1970 or earlier can prevent your iOS device from turning on after a restart.
An upcoming software update will prevent this issue from affecting iOS devices. If you have this issue, contact Apple Support.
It is rather hard to update software on a device that won’t turn on, in this case you need to open the phone to disconnect the battery. It may not be hard to fix but it probably invalidates your warranty, which I can understand some people would not be happy about.
The device fits the definition of being bricked.
