The theory that humpback whales use the stars to navigate the open seas is a fascinating one, but the evidence supporting the theory is not very convincing.
First, there doesn’t seem to be any real connection between intelligence and an animal's ability to use stars for navigation. You know, there are other animals that use stars to navigate. Some birds have this ability, like ducks for example. Now the general cognitive ability of ducks is only average. They are not highly intelligent. The fact that the ducks evolved the ability to use stars for navigation does not seem to have much of a connection to their overall intelligence. It's just an instinct they were born with, not a sign of intelligence. So the fact that humpback whales happen to be intelligent does not make them particularly likely to use stars for navigation. The two things just don't seem to be connected.
Second, there may be a different explanation for the humpback whale’s ability to navigate in straight lines. Remember that for animals to be able to do this, they have to sense some external object or force. Well, the external force the whales could be sensing is Earth’s magnetic field. Humpback whales have a substance in their brains called biomagnetite. Generally, the presence of biomagnetite in an animal’s body makes that animal sensitive to Earth’s magnetic field. The fact that there’s biomagnetite in the brains of humpback whales suggests that they orient themselves by the magnetic field rather than the stars when they migrate.Third, spyhopping probably has nothing to do with looking at stars. Spyhopping is rare, but there are other animals that exhibit it. Some sharks do it, for example. But sharks don't migrate or look at stars. Sharks spyhop to look for animals they want to hunt. And another thing, humpback whales often spyhop during the day, when no stars can be seen. So to suggest that the function of spyhopping is to look at stars is pure speculation.