Even if you account for digital, that does not explain the discrepancy. I'm sure other posters are content with dismissing people as haters or SonyGAF but I'll show you the calculations to see why I've come to the conclusions I did.
First, XB1 games don't sell their majority in the rest of the world. The XB1 is heavily skewed towards the US and UK, and in particular this gen, the US.
Second, Halo has always been a US dominated series. So with those two things said, let's see thr numbers.
Halo 5 sold 1.791 million at retail by the end of December. Assuming a 30% digital ratio in the first month and a 20% for the months after gives us 2.25 million sales in the U.S.
Do you see why 5 million seems unlikely now? Halo 5 would have to sell more in the ROTW then US for the number to be sold-through.
Even if you bumped up the Halo 5 number to 2.5 million, that's still a 50/50 split, which js incredibly unlikely.
XB1 games don't sell 50/50 US/World. They are usually 60/40 at the least. And on top of that, an incredibly US centric IP to boost?
Yea, I'm not buying it unleas Frankie comes back and confirms it was sold-through numbers.