As far as I can tell, the GM Screen has never received errata, and was released same day as the Core Rulebook; the Core Rulebook went through 4 rounds of errata and this was never clarified; and we know that the rules before official launch reflected the deadlier rules, but clearly ended up changed.
I think that all indicates that the lethal version were old rules; the Core Rulebook was always correct; during editing the fact that the GM Screen contradicted the Core Rulebook along with a desire for clarification in the Dying and Wounded rules (referring to the weird unnecessary reminder line) plus having to rush the product out made the mistake happen.
Out of all the places to have to errata, this one is poor; but I'm certain that if Paizo's intention really was to make the game deadlier, they would have done a preview on it. The fact they didn't and instead errata'd it immediately makes me think that the intention was unintended and was only caught by the time full preview PDFs came out.