There is flexible PCV of both clear and opaque types. They do have a "wire" to give them strength and prevent them from collapsing at high suction rates, or being crushed when back-filled. The supposedly have the same rating and qualities of their rigid PVC counterparts (Schedule 30, 40 etc). But they do require some experience when plumbing with them, and are not good for certain situations.

Is the rest of the system "hard piped" with rigid PVC?

Sounds to me like that section might have originally been hard PVC, when it failed the areas between where the repair was needed was too short to put in rigid PVC. So the person opted for flexible rather then make more extensive changes.

The problem with doing this with flexible PVC is, it comes in rolls. With a short piece , it always has an arc or bend to it. It's almost impossible to straighten them in short lengths. The point at which this flexible PVC met up with the glued socket was probably never square and seated in the glue properly.

Even when you plumb with flexible PCV in long lengths, you should arrange and feed it into a glue socket so that it's coming in as straight as possible. Even holding it straight while the glue sets up then letting go, can create a stress that eventually make the bonds fail.

Many builders/serviceman still resist using this product to this day.