That doesn't matter, they were discussing bloodiest battle EVER. As in any time frame, at least he didn't specify a time frame that I am aware of.
So you might as well compare all the battle regardless of time frame or equipment. Like I said, if you compare Gettysburg to Cannea, the battle of Cannea is more bloody. In a few hours (the battle lasted not an entire day but more like half a day, was over by the afternoon) some 50,000 Romans died. The battle is said to have began during the sun rise and been over by the afternoon. So we can assume about 5-8 hours maybe. So in 8 hours 50,000 soldiers died. Gettysburg does not even come close where there were muskets and artillery. In Cannea the Romans and Hannibals army had swords and spears only.
So I'd think I call Cannea way bloodier than Gettysburg, especially with much inferior technology. If you want to go back even further you can look at the battle of Gaugamela (sp), Macedonians against the Persians. Some 40,000 Macedonians against a believed 250,000 Persians.