This is because they *are* using a fish eye lens. It will appear concave and curve the opposite way if your straight line is below the halfway mark of the lens.

I can take a wide lens and make any curved object or straight line appear convex or concave or straight depending on where I place the lens in relation.

This doesn’t really give us anything of value to say one way or the other. They are obviously using a wide lens if you just look at the close up objects and try to draw straight lines.