Simply put... not a northwest trade gun (the gun you mention in the article). The northwest trade gun was the standard smoothbore pattern gun sold to native people throughout all of North America. These were inexpensive guns made in the thousands over a period of roughly 175 years. Here are the particular differences.
The barrel of a northwest trade gun would have an octagon section at the breech that extended approx. 10" forward. It then transitioned to round with the profile remaining round all the way to the muzzle. Your gun has an octagonal profile all the way from breech to muzzle.
A northwest trade gun had a stock extending all the way to the muzzle with no muzzle cap. Your gun is a half stock with a cap at the end where the ramrod enters the stock.
A northwest gun had 2 distinctive ramrod pipes made from ribbed brass fastened to the wood stock. Your gun has ramrod pipes soldered directly to the underside of the barrel.
The northwest gun had a distinctive style side plate. This changes slightly over time but was always a "serpent" or "dragon" shape. Your gun had a simple elongated washer (now missing) for the lock bolt.
Early northwest guns had 3 bolts to hold the lock in place. Later this was changed to 2 bolts... the rear bolt being replaced with a wood screw. Your gun appears to have had 1 lock bolt.
Throughout most of it's manufacture the trigger would be pinned directly into the stock without a metal trigger plate. Your trigger has a plate.
Another distinctive feature of the northwest trade gun was an iron trigger guard with an oversized bow. It was mounted flush with the wood and not inlet. It had distinctive finials at both ends that changed slightly over time. Over most of the guns manufacture, a bolt would come up through a hole in the trigger guard and thread into the barrel tang. This is what held the end of the barrel into the stock. The bolt would be angled and the head didn't fit flush with the trigger guard. What's left of the trigger guard on your gun is inletted into the wood, had a squared end, and is fastened with a wood screw.
What you have is probably a percussion half stock rifle made roughly 1850-1870 in relic condition. The only parts intact are the trigger and barrel.