First off, welcome to YT!
The growth chart you saw is just an estimate. There is no way to know exactly how much your pup will weigh full grown. The breeder can also only make an estimate. I've heard of really small furbabies becoming 7 or 8 pounds. It just depends on if they get a growth spurt or not.
My pup was 1.6 pounds at 9 weeks old when I got him (his two brothers were also small). His parents were 5 and 7 pounds, but he is almost 8 months old now and only just over 3 pounds.
I'm hoping he gets another growth spurt, but there's just no telling. I spoke with the breeder a few days ago, and my pup's brothers are both 4-5 pounds now.