Triathletes are certainly not the most fit athletes in the world. And “fit” doesn’t mean endurance (other than to myopic triathletes). In this case I think the reference is to the combination of strength, endurance, speed, agility, flexility and so on, many qualities that triathletes don’t have (or need). So yeah, I’d say there’s a pretty good argument to be made that MMA guys qualify.