"Smart" could mean a lot of things. Animals can be relatively smart. What makes humans special is out capacity for language. We have the musculature to create audible language, and the specialized neural lobes dedicated to creating and deciphering it.

Language, along with our advanced prefrontal cortex, creates the opportunity for knowledge transmission. I can tell my kids everything I've learned, and they can learn more and tell their kids.

Some animals have some of these abilities. Dolphins have large prefrontal cortices. Whales sing songs with tons of information we haven't even deciphered yet. Parrots can create language. Great Apes can be taught to understand language. Crows make and use tools, and teach other crows to do the same. But so far, we haven't found any animals that can pass down unlimited information the way humans do.

Interstellar space travel would require either super advanced technology or hyper-specific biological adaptations. The idea that whales showed up from another planet and became the whales we know today doesn't make a lot of sense in the revolutionary record. Now, if you said crustaceans or lichen or something were ancient aliens, that would feel more believable.