I don't have a problem with the idea that non-terrestrial intelligences could be non-humanoid in form. But I disagree that any non-terrestrial intelligences must be non-humanoid in form. Or even that it's unlikely for non-terrestrial intelligences to be humanoid in form

Think about how evolution fills niches in different parts of the earth. In Australia there are marsupials (a very primitive form of mammal that have evolved along a different evolutionary path for more than 65 million years since leaving South America before the continents drifted apart). But they evolved along fairly similar lines as mammals in certain respects according to the ecological niche they fill. They're different from mammals from other continents, but they're also very similar in many ways. Function does indeed seem to dictate form to a very large extent.