It was to judge whether concussions would be reduced if football players in the US were to no longer wear helmets, as some have suggested. Rugby League is probably the branch of rugby closest in style of play to American Football, so the comparison is reasonable.

The poster's point was ostensibly to say that reducing the rate of concussions from 0.64 to 0.48 per game would be more or less immaterial. However, that is a 25% reduction. That said, I tend to agree that equipment improvements, rule changes and better enforcement are a better approach to reducing concussions from playing football than removing helmets.