Cleverness, as I understand it, has much to do with a body mass to brain mass ratio. Anything over a certain ratio is beyond what is needed to regulate the body, and so the creature comes across as 'clever' compared to others.
This includes everything from squirrels and cats (at the low end of 'above average cleverness, based on this ratio) to dolphins and chimps (at the high end, based on this ratio). Dogs come somewhere between the two, humans are somewhat off the chart compared to these animals, and squids technically - by the chart - should not be as clever as they are, so something is up with them . . . . Or perhaps their neuro structure (not sure if they have enough neuron mass to actually be said to have a brain or not) is more efficient than we realize - and thus they should be considered higher on that chart than they are.
But what you say is true. Humans below, say, Int 7 should not be considered intelligent enough to go on adventures. By Int 3 they should likely not be allowed away from their guardian or family, as they are basically infants in an adult's body.
On the other hand, those animals likely have a 10+ Wis, and recall that Survival - which includes tracking, trailing, finding food, finding shelter, etc - is a Wisdom based skill. Combined with an Int of 2-6, that is more than enough to out-"wit" some humans (of average Int and average to low Wisdom), especially as some animals have racial bonuses to Survival or other Wisdom based skills.
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