Why would my Mountain Bike tire have blown out?

I rode my MTB over the weekend. I was mostly riding forest roads, and inflated my tires to 40 psi. I did about 28 miles. The weather here was warm for November, but not hot. High was about 70. Later that evening, I went into the garage and found that my tube had blown out and debeaded my tire. Any ideas why this would have happened? I have had a road tire do it when I accidentally left it in my truck on a hot summer day. Can't figure out why the mountain tire would have done that in the garage.

 

Don't think so. The temperature difference between when I inflated and the highest temperature in the garage that day was only 15 degrees. Plus, I wasn't near the max inflation pressure of max pressure for the wheel.

I saw someone mentioned that old tubes could pop in another thread. But I would have thought that would have happened during the ride, not sitting idle in my garage.