I think you probably need to drop this and step away.
As someone with cancer, I think it’s very easy to catastrophise. The consultant may very well have not said this, but stepmum may be incredibly anxious and have catastrophised all sorts from an initial investigation.
I know before I was officially diagnosed, the GP said I think it’s this, then got to the hospital and consultant said, I think it’s this, and then they did the biopsy and it turned out to be something else, and then I had to have another biopsy and the staging changed. I truly thought I was going to die and had less than 2 years. I’m not dead yet and it’s been a year and a half already!
If you’d asked Dh or anyone else in my family, they would have gotten it totally wrong. Even now, I don’t think Dh would be able to explain what stage I am or name the lymph nodes I’ve had removed. You seem like a very invested daughter, but I’m not sure that’s necessarily how everyone is.
My dad died of cancer too and I only vaguely know what sort. It was stage 4, but I don’t know where. If you’d have asked I would have totally gotten it all wrong.
Maybe he’s a weirdo, maybe this is too much for you right now, but I wouldn’t necessarily assume he made it all up. I’d assume he probably just doesn’t know much about cancer. Most people don’t until they have no choice.