Yes its a games sale site, but you are looking far too much into it. MS hasn't signed an oath to this site, they don't even have to tell us anything. There business model is completely different to Nintendo's and Sony's. This day and age, we must start accepting it, a digital world and service especially for the Xbox brand. 1m players is still 1m players who went out of there way to play SoD2 which I would think is a great thing considering the games (Low) budget and sale price.. seems like a win for MS/Xbox.
Does it matter if half those numbers were on Mobile phones, free trails, or forced bundles? It seems many on this site excuse forced bundling so might as well excuse the rest of it. Nothing is ever accurate. Just like Wii Sports for the Wii, greatest selling game of all time.. yeah okay. (I loved Wii Sports, just saying)
It matters because it will influence if people on the fence would buy an xbox or buy the game at all. When a game publisher obscures how well their games are doing, it doesn't speak well for how good the game is. If a game has a price tag, how many people paid for it matters. If a game is part of a games as a service business model then concurrent players who pay matter.
I am still a little confused on why it matters. The general public who buy video games don't ask the store people how well a game is selling for them to make a purchase, nor does a game selling extremely well or not will make that difference. Iv worked in retail long enough to know that customers rarely approach me on how good a game is selling for them to make a purchase. If someone is after a Zombie Survival game than most times they will pick up the SOD2 box and start reading the back info, not how much it has sold in general.
MS are saying 1m people are playing SOD2, regardless of platform, that is a good number across the broad, do we need accurate information? No I don't think we do. Is the game doing well? Well enough for MS to comment on it, that's all that really matters.
Honestly games like SOD2 and Sea of Thieves are designed for Game Pass, its not about the short term sales, these are games that hold 100+ hours of gameplay, this is what MS seem to be focusing on to convince customers to subscribe to Live and Game Pass. The longer the game the higher the chance to increase those Game Pass memberships per month.