lifeguard at the cement pond
That's almost got it. It isn't "those who measured Antarctica" it's "those who claim to have measured Antarctica". In other words, they deny that any such measurement has ever been made or even that it could be made.
Poe's Law is truly in full effect here.
quick thought experiment - if you positioned any number of ships equidistantly around the round earth model of Antarctica and communicated via directed radio waves between them - over the continent - you should be able to use radio directional finders to triangulate each ship as being directly (or obliquely, as the case may be) across Antarctica
in the flat earth model, they'd be beaming their signals out into the void beyond the edge
you could do this with planes and lasers too, i suppose