Hollow earth theory is one of personal favorites, mainly due to how batshit insane it is, and how unhinged the supporters are. They make flat earthers seem like functional members of society in comparison.
No it's just he's a very famous man. It's like saying before Stephen Hawkins died he had a conspiracy theory.
Though really it would me more like Einstein saying quantum mechanics is wrong. It's just a scientist making a hypothesis and then being wrong about it. But the fact it started by such a famous person is kinda cool.
Edmond Halley from the Magnus archives is much cooler. He was forcibly drowned in a pool of absolute darkness belonging to a cult he was apart of and absorbed an embodiment of nyctophobia which he used to swap bodies for centuries effectively achieving immortality until he could somehow find a way to darken the sun. Real Edmond Halley is still cool though