Bluescreens can happen for all kinds of crazy reasons...saying it was automatically the HDD is like the doctor diagnosing you with the flu after you only told him you have a cough.
It could be the HDD, yes. But it could also be related to other hardware components or even software related. Maybe a fan gave out and the system overheated? Maybe a driver failed which had some random issue? Maybe a capacity blew? Maybe his DVD drive is a ticking time bomb? Who knows! In the past 2 months, I've had three types blue screens while upgrading my system: one because of my CPU upgrade, one from my USB Wireless adapter shorting out on its USB cable extension, and one from my graphics card involving .NET framework.
At this point, there is not much we can do for you without more information. If it happens again, try and write down the information at the bottom of the BSOD. It should be listed under the "Technical Information:" header. This should give more information to help. If you really want to know, there are PLENTY of resources on reading BSOD logs listed in Google. Don't be afraid to explore and learn on your own first.