I think that was fans assuming Sansa thinks her rape at Ramsay's hands is the defining event of her life when it's not even in Sansa's top thirteen. As bad as that was, she hated the Boltons much more for killing her brother and mother.
Which shows the rape thing left a much bigger impression than in the showrunner's minds--because it was just a thing they threw in to give Sophie Turner something to do.
People are angered by what Sansa's words imply because said words are being seen as yet another example of the series trivializing the subject of rape.