The article doesn't mean copper alloy tools though, it means copper tools, including weapons. At least that's how I read this:

"Copper was accessible enough and easy enough to work that it allowed early proto-states to reliably arm their warriors with something better than stone weaponry, which often chips or breaks under impact. Copper is a soft metal, hence its use in pipes and wiring today. But it generally won’t break, and though it does bend easily it can also be bent back into shape."

But I think the article is right.