Odds are that that is what happened. The solder joint problem is huge with modern devices. It comes down to a few things. First, as chips get more and more features crammed together, they need more connections to the circuit board. While older chips used pins that went through the board, modern chips rely on "ball grid array" designs. This means the chip has a grid of tiny metal pads on the bottom lined up with the board, each connected to the board with a small ball of solder. The second problem is that stupid government regulations have made lead-free solder mandatory. This brain-dead decision was obviously not the doing of engineers, as lead-free solder has a higher melting point and is brittle while lead solder melts at lower temperatures and is more fluid and softer. The lead-free solder is often "cold-soldered", this means that when the chip and board are heated to melt the solder, the joints towards the middle of the chip do not get hot enough to properly flow the solder and you get "cold solder" joints. These joints are brittle and stressed by heat, often to the point of failure if the device runs too hot or goes through too many heat cycles.
This is nothing new, in fact you've probably heard of at least one incident caused by this effect. The biggest one I can think of is Microsoft's Xbox 360 Red Ring of Death. This is caused by poor cooling on the graphics processor allowing the GPU to get hot enough to weaken the solder. Since the 360 is never left on 24/7, it is in a constant heat cycle and thus was very quick to fail. I've seen many 360's that have suffered from this problem and fixed one using a hot air soldering iron to re-melt the bad solder.
On the PC side of things, I had my HP laptop's nVidia 8600M GS chip fail last year after a similar issue, the chip was very inadequately cooled with one tiny heatsink and I played games on it all the time. Just over a year (and of course the warranty period) the board failed and had to be replaced at my own cost.
This is why I recommend keeping any ball grid chip cool at all costs, even loud fans. I never let my 5870 exceed 60C even if it means a loud fan because it's the best way to keep it safe from the solder failure problems.