A breastfed baby can not take in too much breastmilk. That is exactly the point. The sucking motion on the breast takes up quite alot of effort and energy and as hindmilk is very creamy and high in fat, they will stop sucking once they are full. Many breastfed babies do "passive sucking" even when full, again this is due to psychological factors. Babies have a natural instinct to suckle and if you offer them the breast, that is where they would like to do it.
I don't think the article is saying ALL bf babies are skinny and ALL formula fed ones are fat. My exclusivley bf DS looked massive at age 5 - 6 months. At age 2.3 he is quite short (like me !) but skinny. Other bf babies I have seen are much taller, some are heavier, but these may be due to genetics and food. The age of weaning off the breast and on to solids may also be important. There is huge variation in the number of months/years babies are breastfed and I am certan this can be a key to weight gain. Not all bf babies are exclusivley bf for the first 6 months.
In fact the research says that exclusively bf babies tend to gain weight much quicker in the first 6 months than ff babies. Again there is a scientific reason for this. There are psychological as well as physiological reasons why a bf baby may gain rapid weight in the first 6 months. After the first 6 months bf babies tend to go through a rapid tapering off in weight. This doesn't mean they all end up looking skinny. Genetics and the type of food offered will also play a part after the first 6 months.