While surely you're right that he wasn't asserting that lack of fitness is a self defense "thing," his actual point was confusing. It seemed to be a slightly confusing cause and effect argument about fitness level, athleticism and MMA vs TMA, related to how they prepare. The idea being that MMA guys intend to fight for three rounds, while TMA guys intend to fight no longer than 15-30 seconds.
He suggested that the mental approach is different. I personally agree, but would suggest that preparing to fight for only 15 to 30 seconds just sounds like a terrible idea when the stakes could be as high as life or death. Mental approach-wise, I do know that the approach in MMA is that the fight should never be harder than the training. The saying is, "Train hard; fight easy." And the mentality of gameness is that you will never give up.
Whereas training with the idea that a fight should only last 15 to 30, if you do it right, sets you up to fail. What do you do if the fight goes on for a minute? 5 minutes? 10? Do you give up? Mentally, if the fight for your life is protracted, and you have only trained to fight for 30 seconds, I'd say you may already have given up.
He also seems to conflate a high degree of fitness and athleticism to MMAists but seems to sell TMA guys short. Personally, I've seen some kung fu guys who are just monsters (physically).
I think Drop Bear was being a little flippant, but he's reacting to a position that seems difficult to support.