I never heard of that or how true it is. My son was 11lbs 3oz at his one month check. About that time he started sleeping 4-6hr stretch at night. Right now his sleeping routine is 5hrs (10pm-3am), nurse, sleep 4hrs (3:30-7:30am), nurse, sleep about another hour or so and then up for awhile. He was born 8lbs 2oz and left the hospital at 7lbs 4oz -- we were slow with breastfeeding. His average growth rate has been 1lb and 1/2inch a week.
My son was 11 Ibs at his 1 month check up too, which shocked me because he isnt a big baby, I guess hes just heavy lol. But sadly he will only sleep 1-2 hours at a time :( youre so lucky lol