This is an anecdote.
As far as I know, this is an axiom derived from Euclid's parallel postulate, which you can't prove, but neither you can disprove the existence of such a line.
I may be wrong, it will be good if somebody clarifies this. Thanks.
(maybe it didn't have "straight" in the original, I don't remember, but I don't really know if this matters
)
I don't know much about Bolyai's ideas, neither what Gauss and Riemann did with all this. I have a long time until Riemannian geometry.
I think they've just replaced the axiomatic system used by Euclid and created this new geometry, but this does not "
disprove" Euclidean's geometry?