1 pointHumans notice causal chains when they're pretty young. This means, they start to figure out that when thing A happens followed by thing B, it is a common pattern, and if thing A happens followed by thing C it is probably coincidental. As they observe more closely, they start to understand the other elements in reality that are playing a role, and thus understand certain causal chains not just as "there's a pattern of correlation", but in a more detailed way: of seeing how that causal chain works and leads up to the observed effect. This faculty is reason.
1 pointAssuming the "Indians" never saw anything on that part of the ocean before, it would make more sense that the ships would have been very noticeable, like a some new unaccounted for island or some inexplicable giant sea bird or other creature, clearly never previously seen in that spot and clearly out of place. I'd take whatever you read with a huge grain of salt. Post modernists like to say ridiculous things about perception. Something noticeable and very out of place does not become invisible simply because it is new to one's conceptual framework. It's something new for sure... and perhaps one cannot identify or fully understand what they are seeing... but is it still is a something which is seen. Whether or not and why they did or did not notice the ships is independent of the fact that they never had seen one before... new things are not invisible... if that were so humans would be literally blind as newborns and would permanently remain so throughout their lives.