Anyone who is already putting up 140/100/180 at under 100kg BW is not going to see a 20kg increase in their 1RM in such a short time frame from simply increasing volume. I dont know how freakish some peoples genetics are but if i can gain 20kg on my squat in a year im pretty stoked! When you have full time work and shifts vary etc. gym time becomes more about quality of training over quantity ( less volume using most important lifts only for the highest effort ).
That study like most other studies conducted in bodybuilding/strength training are more based around students who have consistency and time to train when and how they want with little interruption.