"Not believing in coincidences" is a standard canned quip, a meme of sorts, for just about any internet conspiracy nut, used selectively to defend their baseless theories but not actually a principle they apply literally to everything (unless they have profound schizophrenia I guess.)
I know, but it’s useful to point this out. “I’m batshit crazy” is hardly a sound basis for an argument.
I think you're making too much out of it. "I don't believe i n coincidences" is just a dismissive way to say "I don't think THIS is a coincidence." It's not meant to be taken literally.