Ahh, how random.
Similar thing happened to my car a few years back.
When I first got it I had a new motor put in it, and while the mechanic was out on the test run it died.
Towed it back and call the auto sparky out the next day. Checked the car ovr (I have no idea how long he spent), but it turned out the earth on the fuel pump had come loose.
Very random thing to happen, and I'm glad it didn't happen while I was driving her.