Good grief. I was a pro VR photographer for ~15 months, doing stitched-spherical panoramas. I am *fully* aware of optical and projective distortion effects and how to accurately characterize and correct them.
Yes, pretty much all camera lenses (especially wide-angle ones) produce some degree of radial distortion - barrel, pin-cushion, or moustache (compound).
However - fun bit of trivia: 1/
because radial distortion is *radial* (ie it only affects the distance of a point from the lens's optical center) any actually-straight lines passing through lens center remain projectively-straight.
You are also conflating lens distortion with external effects (ie air refraction) - which is a real thing, but also mostly predictable and correctable. Further, because the effect of standard air refraction 2/
is to progressively *raise* the apparent location of objects by distance, it is easy to show that images below horizontal must be of objects *further* below horizontal.
If Earth were truly flat, the effect of air refraction would be to make it look concave - like standing at the bottom of a shallow saucer. 🤔
GSV_Empiricist