I think that's revenue and not units sold, at least that's how this sounds to me:

"All of that offset a 4 percent increase in spending on PlayStation 4, Xbox One, and Wii U."

"Spending" sounds like revenue to me.

Edit: OP already got updated

PS4+XB1 = 2.9mil if this guy's math is correct http://www.neogaf.com/forum/showthread.php?p=192222426#post192222426

What am I misunderstanding?
Selling software is the main profit outcome to hardware developers as well, breaking records in selling software is undoubtly a mark of a good month for everybody.

Shadow1980 said:

 The first three Gears games did pretty well. They all charted in the Top 10 for their respective release years (2006, 2008, & 2011). Nothing has really hit the series in a way to cause it to bleed a large audience like what has happened to Halo.

Halo is an interesting case. It was once a massive seller. But Halo 5 saw a ~70% drop from previous games for launch month sales. I think this is symptomatic of a general malaise that began afflicting the series since Bungie left MS and was replaced by 343 Industries. 343i's first act was issuing a divisive title update for Reach (I personally hated it). Then Halo 4 did something (perhaps various gameplay changes) that drove off its multiplayer population in rapid order. It took less than two months for it to fall out of the top 3 most played games on XBL, within six months it had already fallen out of the top 5, and within a year it had already dropped out of the top 10. Meanwhile, it took Reach almost a year to fall out of the top 3, and it hovered at #5 to #6 until Halo 4 came out. Halo 3 stayed in the top 3 until Reach came out. Halo 3 and Reach both dealt with competition for time with many other games, including the annual releases of COD, AC, and the various sports games, as well as miscellaneous other big titles released in their heydays. Halo 4 obviously had something specific to it that caused players to leave in droves. Personally, I played Halo 4 considerably less than I did prior Halo games, and that's because I simply didn't like many of the changes 343i instituted.

Then the Master Chief Collection happened. Matchmaking was utterly broken for months. It was finally fixed, and once it was it was really fun, but the damage had already been done. While 343i promised to make right by players in Halo 5, what we got was a mixed bag. The game functioned fine at launch, and matchmaking finds matches very quickly. 343i also kept their promise of bringing back the level playing field that defined the series' multiplayer but was ditched in Halo 4 in favor of COD-style rank-based unlocks and custom loadouts. But at the same time they radically changed the core movement mechanics of Halo (thruster packs, ledge-grabbing, and sliding, among other things, are all default abilities now, and it drastically changes the way Halo 5 plays compared to the other games) and they tossed out split-screen in order to attain that Holiest of Holies in modern game design: a 60fps frame rate. The lack of split-screen alone was enough to discourage two friends of mine from even buying the game. I bought it, played the campaign once, played a fair amount of multiplayer for the first few weeks, but now I'm already tired of it. It's like Halo 4 all over again. I just don't care for the gameplay changes, and I don't feel the same compulsion to play every day like I did with Halo 2, 3, and Reach.

I think a lot of people have just been burned one too many times by 343 Industries. It's the only plausible explanation for the massive drop in sales. Now, by general AAA standards, Halo 5 still did well, but by Halo standards those sales figures are just pitiful. Time will tell if 343i can win back the audiences they've lost, but if Halo 6's sales aren't appreciably better than Halo 5's, I think it's safe to say that the days of Halo being a massive sales juggernaut are officially over.