That's not actually what he wrote. He wrote, "A fare which consists of three-quarters of vegetable food and one-quarter meat would appear to be the most satisfactory for the people of central Europe. Every one should and can find out which diet best suits his constitution, and he should avoid all food which disagrees with it."
Basically, figure out what foods you responds best to. Some lifter do well low-to-no carb, some do IIFYM. Some lifters do well with intermittent fasting, some guys do 3 bigger meals a day, and some do 6 smaller ones. Magically, it all works.
I guess you missed the part where Hackenschmidt wrote:
A few paragraphs later and around the same time, he writes of being measured at 5'9 1/2", 14 stone (89kg/196lbs). That's with about 1,200 calories just from milk. He was eating plenty, don't worry.