He’s always been atheist and looks down on people for holding religious beliefs (he announced to his mother that he wasn’t going to church anymore when he was 7). In his old age he has become susceptable to propaganda. Largely because he doesn’t like immigrants and the sort of news media that agrees with him is propaganda. The British media is full of anti trans propaganda at the moment so he’s just following that. He mostly stays within his bubble of rightwing stupidity with his geriatric rightwing friends.

In short he’s an atheist living in a rightwing echo chamber who’s given up on critical thought.

I know a couple lesbians who, while otherwise as liberal as is stereotypical for the community, are vehemently anti-trans. I have been told by some gay friends that this is more common than one would think.