Cosine similarity is the dot product of vectors that have been normalized to lie on the unit sphere. Normalization doesn't alter orthogonality, nor does it change the fact that most high‑dimensional vectors are (nearly) orthogonal.
In d dimensions you can have d vectors that are mutually orthogonal.
Interestingly this means that for sequence lengths up to d, you can have precise positional targeting attention. As soon as you go to longer sequences that's no longer universally possible.