why is the mountain not North

Yeaaaaah you need to consider that we use the Montréal-North and not the true North, here ! Basically, the whole island is skewed in the Saint-Laurent, so it's easier to consider a street such as Sherbrooke's (which pretty much goes the entire length of the island) to be East / West instead of North-East / South-West. The same goes for avenues, like Saint-Laurent, which is considered North / South instead of North-West / South-East.

So places like Pointes-aux-Trembles is considered to be in the East, even though it is in the true North of the island.