What I mean is that it would be hard to collectively keep a secret that ivermectin works. Your acquaintance's doctor happened to prescribe it - but I'm guessing most doctors would not. So this pharma exec (or researcher, or whomever) would need to tell their family to go find a doctor willing to prescribe it, or would send information to the doctor to convince them to prescribe it, or something. And that would leak.

Also I'm mostly referencing the idea, which I believe I've seen in some of these papers, that people should take ivermectin on an ongoing basis to protect against getting infected in the first place. If I were a pharma exec who knew that ivermectin secretly worked, I wouldn't want my family to get sick at all if I could help it - I'm pretty sure no paper is claiming it's 100% effective, it just reduces the chance of poor outcomes. So I'd have to tell them to find a doctor willing to prescribe ivermectin even before they're sick, and that would definitely leak.