My understanding is that there were two jurers who were unconvinced about the prior art thing. It seems to me like what actually happened is that, rather than trying to convince those two jurers (i.e. coming to a unanimous decision), they just went with "majority rules".

Of course, there's no evidence to suggest that's what they did, but equally there's no evidence to suggest that they eventually went back to that question and debated it further.

Given that they admitted to ignoring the instructions on punitive vs. compensatory damages, it's not a stretch to imagine they also ignored the instructions on coming to a unanimous decision.