This is the oldest evidence of people starting fires

We didn't start the fire. (Neanderthals did, at least 400,000 years ago.)

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[SinclairZX81]

I can't help but wonder if those early firestarters discovered the sparks from pyrite and flint through bored fidgeting with rocks, or if they were trying to do something else when they saw the same sparks that could spread fire over small barriers and gaps.

Probably the latter considering how often flint shows up in paleolithic technology.

It struck me reading the article - and this is nothing more than pure amateur speculation, so you're getting what you paid for it - that fire-starting probably came about in relation to the process of creating stone tools. It's not like we magically "knew" flint was the way to go. There had to be some experimentation, even after the "industry" had settled on flint. So there was probably a body of knowledge that "hitting that shiny stone makes pretty sparks." It just took someone, either by thought or by accident, to realize that those sparks could ignite dry grass or leaves. Once you have that leap, the natural human tendency towards, "Do it again! That was cool! Do it again!" (or however that translates into Neanderthal or earlier hominin) takes over, and soon everyone's doing it.

EDIT: From the several ninja's ahead of me, it would seem I'm not alone in this thinking.