I didn't see brain size linked directly to diet here, only saw it on the infographic. In another study recently, I saw brain size linked to the challenge of hunting large animals (like cave bears and mammoths)
That’s interesting because I’ve also read that animal brain size is positively correlated with group communication and social network size. In order for early humans to successfully hunt large animals, especially large predators, I would imagine it would take quite a lot of group communication and coordination.