If "Humanoid Aliens" exist at all, them having similarities to humans could be due to Convergent Evolution:
https://en.wikipedia.org/wiki/Convergent_evolution
Convergent evolution is the independent
evolution of similar features in species of different periods or epochs in time. Convergent evolution creates
analogous structures that have similar form or function but were not present in the last common ancestor of those groups
Basically another species with completely different biology and biological origin, could develop similar anatomical "Structures", due to evolutionary pressures.
Any Technological "Space Faring" species , would need certain anatomical features to be able to manipulate the elements of their environment to even develop technology.
The "Humanoid" body plan, seems to be a prerequisite(on this planet) for the technologies we've created.
Being "Smart" alone isn't enough.
Being "Smart" and "Dexterous" (hands, fingers, etc...), is required (from what we know) to build complex machines/tech.
Though I'm 50/50 on if Aliens exist, and traveling to Earth, I do understand (from my studies), that a "Humanoid" form is certainly a possibility.
