I have not read this article.
Unless there's lost knowledge of ancient guns, the mainstream history is that gunpowder was discovered in China between 600 and 800 CE. The Chinese would use it to create fireworks, rockets and more topically, they weaponized it in the form of the fire lance(essentially a bomb on a stick). The grandfather of firearms would not come until later, in the form of the hand cannon(also invented in China).
Once knowledge of gunpowder and hand cannons spread to Europe in the middle ages(1200s-1300s), then the hand cannon started to evolve into something more mechanically complex and more closely resembling firearms as we know them today. The pre-musket Arquebus and Culverin were invented (more like innovated) in Europe, with the former being most gunlike of the two. It featured a flash pan and trigger group, making it more of a "gun" than a cannon.
So it depends how you define firearm. If you go by the textbook definition of it being a man portable device that launches projectiles through the ignition of an explosive charge then they were invented in Asia.
Otherwise, if you require a trigger and a firing mechanism that isn't a match and a length of fuse, firearms were innovated in Europe.
