Read it again...
Cruz is saying that it was settled science that the world was flat and Galileo said otherwise, making him (Galileo) a heretic and a flat earth denier.
The theory that the earth was flat was disproved before Galileo was even born.
Galileo was labeled a heretic for claiming the sun was the center of the solar system and not the earth as was then commonly believed.
Galileo had nothing to do with the “flat earth” argument.