Now this is a partially true statement.  Both for flat earthers and ball earthers.  The limits of human vision do create some illusions that are being attributed to both ball curvature and to flat observations.  It is however a more correct statement to say our "field of view", or "our perspective" is influenced the what appears to be a convergence on the horizon and then a vanishing point.  These are statements of fact from simple observation.  Look down a railroad track, or down a long hallway and watch the tracks or hallway converge at eye level to the point you cannot see any further.  That is just how our vision works. This we know.

But here is where that idea does not hold water.  Once you use technology to see beyond you human limits, AND what you can see is impossible using ball earth math due to the "supposed" curvature of the earth.  You now have solid evidence that the curvature that should be both observable and measurable does not exist when an optical aid is able to show you the impossible on a ball earth. 

So your statement is true on a rudimentary level, but once you dig beyond the cursory and begin to test the cage we live in and the ideas we have about this cage then things start to get interesting.  You just have to decide which pill your going to take, the red or blue one... One you stay in the matrix and eat the good noodle soup, and the other opens the door the the world of the "real".  It is up to you to decide...