We dont need to spoiler that, they are directly mentionning it more now to give it teeth as likely scenario (suddenly Rhaegars name regurarly brought up by several), but its obvious Ned Stark isnt truly the father of Jon, been the most realistic and likely rumour since the beginning that he's Neds sister and Rhaegars offspring, and Ned the honourable (him cheating, really?) just took him in as his bastard to protect the kid, and his sister.