Yes, GPU timeouts can cause a crash....and about 99% of those crashes are freezes, screen doing funky colors, or locking up, NOT REBOOTING THE SYSTEM or SYSTEM SHUTDOWN.....
What most people don't realize is that modern operating systems are designed to "crash" in such a way for most drivers that it will restart in session and when it doesn't, the system MOST TIMES doesn't restart itself and requires a manual restart. A system that is turning itself off, or rebooting without user input is USUALLY HARDWARE....it gets tiresome on my part to know this info, and have repeatedly had people come back later and explain that their hardware did indeed have an issue AFTER denying it at the time. Now Messoram_Lopus is very correct, a software issue would be in many ways better than a hardware because of cost and likely ease of fixing.
Now there is a setting in Windows that allows for automatic restart after a bluescreen....most people don't have it set this way, and usually most people know when they get a bluescreen....... Are there exceptions to the shutdown/reboot being hardware, sure there are exceptions to just about everything in life, but in GENERAL, reboots/shutdowns are usually hardware.