Butterfly effect refers to a drastically smaller change than a massive volcanic eruption significantly impacting global weather. The point is differences that are hard to notice making a difference.

Lorenz discovered the effect when he observed that runs of his weather model with initial condition data that was rounded in a seemingly inconsequential manner would fail to reproduce the results of runs with the unrounded initial condition data. A very small change in initial conditions had created a significantly different outcome.[2]

Wind speed of 2.56789281 MPH vs 2.567892811 MPH is hard to accurately detect, but it’s important. That’s the butterfly effect.

I think the point here is that a volcano erupting (according to the wiki the most powerful eruption in recorded human history) triggering a global climate catastrophe is not a "small" change.

Yes, and equally to the point, its consequences were in retrospect big and rather predictable. The butterfly effect refers (colloquially) to seemingly small causes (butterfly wings fluttering) leading to big and completely unpredictable effects. Nothing involved with what we're talking about is similar to the butterfly effect... except in that there was a cause and an effect.

I realize this is all a bit silly to go on about and there's no conceivable future where the OP sees the egregious error of his ways and ritually disembowels himself, or even, you know, starts using the term properly.

Long chain of causation from A to Z, where A and Z are not intuitively connected.

Also, volcanos are pretty chaotic themselves.

Non-butterfly would be: due to increasing population size and a growth of cities and long distance commerce, people invented cars. A very stable reason, not reliant on something fragile.

Butterfly: the balance of magma happened to be in a certain particular configuration, which ultimately lead to a revolution in our lifestyle. Had the magma been slightly different, we'd be on horseback.

Again, maybe the story above does not add up, but if it does, it deserves to be called butterfly.