They may be right on how far human physiology can go, however, they are claiming that all records will end or not be broken because everyone will reach this limit.
This is a very narrow assumption that a sport is all physical. Natural genetics, training, mind set and sheer talent can and will affect many sports more than just sheer musculature.
Take our hobby for example: I cannot paint like Fluffy, Alexi-Z, or numerous other painters, and I have years or even decades of experience over some of them, they beat me through sheer talent, and even if I were to work up to their level they would surpass that level in the time it took me to reach it.
Some people are just innately talented.