I'm always of the mindset that something would have caused this, and it didn't get remedied in time. I always visually check the accessory belt at every service for any signs of poor tracking, splitting, fraying, etc. I also always check the alternator pulley clutch. And of course listen for any noises. I'm probably more scrutinizing as the timing belt interval is coming up.
The CR TDIs, having a longer interval, might require a bit more scrutiny for things like this, especially after the first one, but before the second one, if that makes any sense. And it probably is a good practice to just replace the tensioner, the idler, and the alternator pulley as a precaution and the second interval, assuming they've made it that long. I've got a 2013 CJAA here that made it to 160k mile, and its alternator pulley clutch is locked. The only sign is a slight rattle/wobble noise at idle, worse when cold (when the alternator load is the greatest). It was here for its 160k PM, and I caught it. It wasn't bad at 150k. And the belt was replaced at 120k when I did the timing belt.
This is why I cringe when DIYrs that maybe shouldn't, or worse, quickie lubers, are the ones tasked with maintaining the car. Because stuff like this gets missed. I see stuff every day on cars that come in here that need to be addressed and haven't, simply because the owner didn't know.