Yup, Roman Rowers were not slaves. Galley slaves didn't really become a thing until the middle ages. Not only that but, rowers were considered part of the Roman navy, they could be citizens or non-citizens, and if we're not citizens, they would be granted citizenship upon retirement. That meant that any children they might have (of a legal marriage) would also become citizens. Despite the demanding physical labor, it was not considered a bad deal.
Rowing of course was terribly hard, the rowing space was cramped, hot, and noisy. The work was physically demanding and literally repetitive. The most senior rowers got to sit on the top row closest to the deck above them, which gave them control of the oar and the most fresh air.
On one notable occasion, Octavian was in need of more manpower, he asked slaves to row, however, everyone who volunteered for the job was freed before they entered the ships.
If you're interested in more about the roman navy I highly recommend the works of Micheal Pitassi. who has three easy-to-digest books on the subject.
"The Roman Navy: Ships, men, and warfare 350 BCE - AD475" was my favorite of the bunch, followed by "The Navies of Rome"