Please don't think I'm bashing or nitpicking, but want to ask you some questions so we can understand the failure.
1. Most manufacturers recommend replacing a tire at five years. Yours was just a little over that based on your post. What was the actual four digit manufacturing date on the tire? Even though you may not have a ton of miles on it and the tread may be in good shape, the carcass may have failed due to age.
2. You say your were running 72psi in your load range E tire? Did you know the actual weight the tire was carrying in the position it was mounted? Did you adjust the pressure based on this weight, and if so what table did you use? Why not inflate the tire to 80psi when cold which would have give you the maximum weight capacity of the tire?
3. Had the tire ever been repaired? If so, it could have been a contributing factor to the failure.
4. Was it the left rear or right rear tire? The reason I ask is that the right rear typically bumbs more curbs during its lifetime than the left rear.
Jim