Especially against Battlefield 1. EA was running a massive marketing push, and it was also smack in the cultural zeitgeist with the centennial anniversary of WW1. it felt like half of Youtube was connected in some way from gaming creators to historians of all stripes.
Combined with the fact that it had been 5 years since the last 'real battlefield' game, with hardline not having much staying power, and 1 being the first game for the PS4/XBOX 1 generation of consoles (4 was a cross generational release) I don't think anyone was shocked when the sales figures were through the roof.
