Crucially Norway doesn't use "winner take all" voting and people are able to express more nuance in their preferences, otherwise Norway would also have 2 parties. When most Americans hear "multi-party system" they tend to assume voting works the same way as in the US, but that somehow other countries reach a different equilibrium with the same inital conditions.
Canada has a parliamentary system with winner-takes-all for each seat. We have three major national parties and a regional party which regularly has a significant minority. The system is not fundamentally different from the one used to select representatives in the US. Many other countries have similar systems, but not all of them have two party rule like the US.
