The IQ is because smart people breastfeed thing has been discredited, IIRC.
And as you are probably aware, not breastfeeding doesn’t make (genetically-prone to being) smart people STUPID. So yeah, your brother could have been, um, exactly what he is. The difference of a few points one way or the other when you are already pretty damn smart isn’t going to be really obvious. I find that reasoning (‘so and so wasn’t breastfed, but he/she is brilliant/healthy, therefore breastfeeding isn’t all it is cracked up to be’) just as annoying as the ‘if you don’t breastfeed, your kids will turn out sickly and stupid’ routine.
The statistical difference between breastfeeding and not is 1) primarily seen if breastfeeding is done longer than 8 months, 2) even then only takes it to a single standard deviation’s difference (11 points on the WAIS scale). In other words, it is measurable, but for most people it won’t make a noticable difference. Where it does make a visible difference is when people of lower ‘expected’ IQ were breastfed (preemies with brain damage, for example). The difference between 70 and 81 is significant for function, autonomy, and success. So is the difference between 80 and 91, and 90 and 101. Once you get to 150 vs 161, chances are nobody but someone above that level is gonna notice or care. But even if you get 4 or 5 points difference at the lower end of the scale, you’ve got a real benefit.
And no, that doesn’t make anyone who couldn’t breastfeed their mentally disabled child feel any better. I do wish that banked milk was more readily available in the US - the WHO considers it the secondary food source for all babies who cannot have their mother’s milk. Formula should technically come third, but we have only… I think six(?) milk banks in the entire US? I know plenty of women who would donate if there was any functional way for them to get the milk to the bank. Even pasteurized, it helps.
Sigh. But in the meantime, anything they can do to improve formula is a good thing. Humans are pretty resilient, and women have been using milks other than their own on their babies for centuries (Soranus, 2nd c. AD Greek OB/GYN encouraged women to breastfeed for at least 6 months, or find a wetnurse, rather than going straight to goat milk or giving pap or cereals… and he describes women who just dislike breastfeeding, and those who struggle with it, and whose babies won’t latch, etc… this ain’t nothin’ new!). And we’ve survived pretty well.
Frankly, the IQ think also leaves out a major issue of parenting - teaching your child to use their intelligence intelligently. That makes much more difference than what their raw score is, IMHO.