This is a repeat of a prior Tesla publicity stunt. What they do is they only ship cars to Norway quarterly, and by filling a big backlog of orders they then claim to be the most popular make in that month, which is technically true but also quite silly. You can clearly see on the graph in the article that the reason Tesla "sold" a ton of cars in September is because it sold almost none in August and July prior. And Tesla has been pumping this PR trick for at least four years.
I think this says more about Tesla's bizarre production and delivery schedules than it says about the automobile market in Norway.