I don't see anything or am I missing it, about at what age did they determine the sex of the tortoises? They all look female until they are older, 3 plus years.I would say that this is the result of a limited data set. This graph presents their results that one clutch of eggs incubated at 32.5 C resulted in 0% males. This is just the result of one experiment. Your results may, and will, vary.
Breeders "incubate for female" and frequently end up with all males, .