I still don't agree about herbivorous diet not selecting for intelligence. There are still benefits to being intelligence even if you don't eat meat, some of which I already mentioned, but which also include complex social behavior and survival skills. You are completely right that carnivorous diets can encourage this perhaps more often, because if you're hunting larger animals then you usually need some skill and maybe a little organization/cleverness, depending. However, there are still plenty of reasons that aren't hunting-related to evolve greater intelligence.
Chimpanzees do engage in some hunting activity, but is that why they're intelligent? I honestly don't think so, as their social intelligence and cleverness, as with that of other primates, simply doesn't seem geared towards that very much at all. If you observe how primates act and what they actually use their intelligence for, it is largely for things that have nothing to do with hunting other animals. This alone should make it pretty obvious that intelligence can be selected for for plenty of reasons that have absolutely nothing to do with eating meat. Monkeys use tools, communicate, can actually engage in planning behavior, can learn very well, can learn from each other, and so forth. This doesn't just help you hunt things. It helps you eat a wider or healthier variety of vegetation (because you figure out what you can/can't eat, what's helpful to eat, complex tool usage for cracking harder nuts, etc.), helps you avoid and fight off predators and rival groups, encourages more complex organization of the group in general (which is beneficial for a variety of things), etc. I simply do not believe that the only reason primates evolved higher intelligence was because they had to hunt, for two reasons: One, I don't see much evidence that their immediate ancestors did that much hunting, and two, pretty much all the higher order primates exhibit a similar sort of intelligence that is beneficial and could easily be selected for whether they eat meat or not. If an herbivorous animal benefits from intelligence, then how can you think intelligence can't be selected for in creatures who are herbivorous to begin with?