I was confused as well. I don't recall seeing this the first time I read the article, but on the second time through, they include this:
"Our research reveals that Plimpton 322 describes the shapes of right-angle triangles using a novel kind of trigonometry based on ratios, not angles and circles. It is a fascinating mathematical work that demonstrates undoubted genius."
Which is probably where the "more accurate" statement comes from.
I just thought about what strategies they could actually take without being able to communicate information or use the outcome of the others flip as an input to their decision. There are only a few things you could do- guess either heads or tails every time, guess your roll, or guess the opposite.
Then I realized if one took the "guess same" strategy and the other took the "guess opposite" strategy that would cover the bases.