As I stated prior to the quote you posted, the scale is off. In the pictures the OP posted, he had 5 pieces of rock weighing in at 4.5 Lbs. To be a truly accurate example, he would need to use 20-25 pieces of rock that totals 4.5 Lbs. This would be realistically scaled down example of a larger tank.
I've got some smaller pieces in my sump if yall want me to weigh those and toss them in???