This is definitely a real effect. I can’t doodle this out right now but if you grab a piece of paper and draw out the triangles for a pinhole camera with differ

This is definitely a real effect. I can’t doodle this out right now but if you grab a piece of paper and draw out the triangles for a pinhole camera with different focal lengths you can see how the angles (and horizontal separation at the image plane) are quite different with different focal lengths.