Thankfully, the nature of a revo blowup is for the forces to go forward and perpendicular to the shooter.

It's hard to tell without being able to study the parts firsthand. Just from the pictures it looks like the barrel had a crack or inclusion that gave way.
In the picture looking at the back of the barrel you can see the surfaces of the split on the right side are a different color than those on the left. The left side is a new break, the right side has brown discoloration where the metal was not homogeneous for a period of time before the break.

The gun appears to have timed up correctly when cocked single action, and there is no bulge in the barrel to indicate a blockage.

My vote is an imperfect piece of material that the barrel was made from.