Implication in the quote that he thinks you didn't read past the headline. But I'm going to suggest he may be pitiable - it could be that he's subconsciously afraid to start re-evaluating his priors. Probably a common problem over there nowadays.

To make a classical reference, the allegory of the cave as written by Plato, describes a possibility. You've left the cave and seen the true world, returned to the cave to bring freedom and enlightenment, but the others in the cave lash out at you in response. Such things get compacted in various memes, like the red pill stuff.

Put another way, your father's probably happy or content with his worldview and he sees an unhappy person advocating for a different view (and part of his worldview is probably that all alternatives are lies), so he'll think that taking this view will remove his comforts. I add the parenthetical so you aren't misled into thinking your happiness would lure him out of the cave.