That'd be it.
If you would buy yourself a ticket on some spaceship like the Soyuz and you see a roudn earth, then it probably only appears that way.
If you prove that the Earth is round using proven mathematics and geometry, then it just appears that way.
If you can see satellites, if you can experience the seasons, if you can see the stars rotate, if you can see a ship slowly sinking down the horizon, if you can land on the moon ant tell the Earth is round, then...
it probably only appears that way.