I'm not sure if it's a thing about the baby sleeping through the night at all to be honest. They were talking about the parents, so think of it this way (in very general terms)....

BF mum gets up, whips out a boob & you're off, then puts bub to bed & nods off herself, no need to fully wake up really. (Although not being able to BF first time I'm not sure if there is anything else in there?).

FF mum gets up, goes to the kitchen, gets the bottle, heats up the water, mixes the formula powder in (which has to be exact), feeds baby, puts baby back to sleep, back to the kitchen, rinses the bottle, back to bed. You have to be totally awake to measure of the formula or you're in trouble & it takes longer to get back to sleep from fully awake.

So yep I definitely agree with the study!