O-rings aren't just for engineers. It's a standard part use in many everyday scenarios, not just rockets. You can buy them in the hardware store. The cladding is most certainly not an o-ring, even to the layman.

Rather, the writer probably used the word o-ring specifically because of association with the Challenger disaster. They probably remember (maybe subconsciously) a lot of discussion of o-rings in a disaster back in the day so that word popped into mind when describing a part related to this disaster.

All rings I've seen were o-shaped. So I think there is no need to add that aspect.

the "o" in o-ring refers to the cross section of the ring if you slice through it