[stormbrew]

I don't think discover implies anything about the effort put in on its own. If anything I'd say it leans towards deliberate effort, even if not always an expected result.

If it's just a fluke then more often and not I'd expect to see that spelled out as either context, or with the words you used: "stumbled upon".

At any rate, I think the reason it's used in this context in particular is because it represents that the 'equation' is not just a mathematical construct someone came up with, but that it represents observable reality in a way that is novel and perhaps unexpected. It wasn't something someone made up, it's something that usefully describes phenomena that are outside human control. Thus, they did not invent, instead they discovered.