could you take a close-up pic of the blown out section of tire? i'd like to see the bead breaker strip and what may have happened to it.
thx

The brake pad hitting the sidewall is the most likely culprit. When the brakes are applied and they will bend and rotate counterclockwise, so the top-front of the pad would be the most likely to make contact. Or it could happen when just riding if the pads are high and the wheel flexes enough to make contact.

Or maybe the rip in the tire occurred right after the blowout, while the tire was sliding on the ground. In which case there should be some other damage that was the original cause.

Not seeing how an opening like that could appear on a sidewall spontaneously... cutting across the cords...

BTW... there isn't a chance in hell that tube "stayed inflated"... unless he commonly rides with 1psi. It just has twisted and trapped some air. There has to be a big hole in it somewhere.

_________________
formerly rruff...

That could happen if it were a front brake, but rear brakes arms, being behind and below the mouting bolt, tend to bend downward as they bend forward.

But maybe there is another brake actuation dynamic at work here. On dual pivot brakes, the right arm on the rear brake rotates on a offset pivot. Because the pivot is offset further form the center than the pad/rim contact point, when the brake is actuated the right pad will move in an arc inward and upward. As the pad wears, the arm moves even further in the inward/upward arc, and if the pad worn down too much the shoe may actually arc upward far enough contact the tire.

So, I guess the questions are: Are the pads worn down on the brakes? When the brake is actuated, does the brake shoes arc upward enough to contact the tire?

It looks like the FD cable has a huge amount of excess on it, and it's got a sharp bend in it. Could it be the culprit, if it lost the cable end and got caught?

I had a similar blow out. In my case the brake pad was too loose and had rotated slightly upwards causing the edge of the brake pad to cut into the side wall. Like others have mentioned, this might be your case.

The most common cause for sidewall damage is from cornering. Leaning the bike over in
a corner places the paper-thin sidewall dangerously close to the road surface allowing small stones
or other sharp bits to make contact with the tire's wall nicking a few threads. Miles later, maybe many,
the compromised sidewall bursts open without warning like a defective zipper. It would be very
good if tire manufacturers "locked" their threads so they can't run like cheap pantyhose when threads get cut.

*Update: Brought the bike to the dealer and inspect to see the cause. They concluded that the tire failed, no brake pads or cables caused an external cut on the tire. Again the tube still has air, no hole/tear. The shop contacted continental and told me they were very concerned and currently reviewing the pictures taken by the shop.

It will be interesting to hear if they are prepared to pay for the new Zipp rim you are going to need.