Yeah. I can imagine scenarios in which people would have left the other lane clear; and I can imagine scenarios in which they either abandoned their cars, or died in them. I'm having trouble imagining one in which both of those things happened.
-- on the other hand, as has been pointed out, if there weren't a lane clear the cat tank wouldn't be able to get through.
OK, trying hard: there was still enough sense of order, or enough police presence, to keep the other lane clear for some time; but there was such a traffic jam that people ran out of gas, and once enough cars had done so that it was clear the lane wasn't moving, people climbed out and walked. By the time order/police presence broke down enough that later arrivals moved into the other lane, there were very few people left who were still in shape to drive and who could manage to get there, and those few succeeded in crossing the bridge, so they're not there to block the lane.
ETA: I still don't think that's very likely. But I suppose it's just barely possible.