I remember reading this story, vividly. It had some classic black and white pictures.
The story is about an ape-like (small & slight I think?) alien that lands what I remember as a forest. They get found by some people, and taken in as a curiosity. Eventually the information of this alien gets out, people laugh at it because it looks like some kind of animal and it's told to walk on four legs, even though it is bipedal. I remember it may have tried to convince some scientists of its intelligence by doing maths, only for the scientist(s?) to laugh it off as impossible.
It manages to escape this zoo (I think) and the part of the story I remember quite clearly: it describes that the last time this creature is seen this poor being, lost, unable to get home, crying and trying to walk on four legs in the forest.