That's also the year Kinect was released, and despite what some people think about it here, it was a big sales boost for Xbox 360.
Without some new fangled reason show at E3 this year that we all MUST own and Xbox One, I don't see how Xbox One can reach those numbers. They didn't make a single game that took advantage of the new Xbox One's Kinect 2.0. And rumor aren't so good about Hololense either.
The way Nadella is handling Microsoft right now I would be pleasantly surprised if they do anything new with hardware. He seems bent on making money with business at the cost of everything creative Microsoft usually does. It's kind of sad to watch unfold.
I'm actually one of those that's not convinced that the Kinect did much for 360 hardware sales. I can't say it did nothing, but I can say it's effects appear to be overstated.
Looking at YoY sales for the U.S., the 360 got a massive YoY boost in June & July (+87.7% and +118.6%, respectively) thanks to the 360 S, but that YoY boost dropped afterward, which is consistent with other similar releases (e.g., the PS3 Slim) that gave strong initial YoY boosts for the first month or two, with subsequent months having smaller (but still strong) YoY boosts. However, Nov. 2010 got a bigger YoY boost (+67.7%) than September (+37.3%) and October (+30.2%) did, though only slightly better than August (+65.6%), and that's without the benefit of any big Black Friday price cuts (which really didn't begin in earnest until Nov. 2011). Meanwhile, December's YoY boost was only +42%, slightly above September's, and every month in Q2 2011 got a smaller YoY boost than any month in the June-Dec. 2010 period did. That suggests that the Kinect may have helped during the holidays, but its effects disappeared by January 2011. The 360's performance in 2011 appears to simply be continued momentum from the 360 S, which is consistent with the equally long-term boost the Slim gave to PS3 sales.
That being said, since Kinect did figure into holiday period sales in 2010, it is relevant when making comparisons for the 360's 2010 vs. the XBO's 2018. While it wasn't anywhere near as big of a factor as the 360 S was, it does add a bit more to an already insurmountable obstacle for the XBO. The XBO has nothing this year in terms of hardware or major software. The XBO S and X1X have already released, the former already being over a year old now and with rapidly diminishing effects on sales and the latter appearing to not have done much besides a slight assist for this past November. There are no new peripherals that will help. Halo 6 is looking to be a 2019 release, and that's the only forthcoming exclusive I see that will have any effect on the XBO's sales (Sea of Thieves, State of Decay 2, and Crackdown 3 are unlikely to move any appreciable amount of hardware, and Forza is not a system-seller). The best thing the XBO has going for it this year is the potential for a permanent price reduction to $199, though even then I'm not sure such a price cut will match the effects the S-model had on 360 sales in 2010.
TL;DR, the XBO's surplus over the 360 will start disappear very quickly once June rolls around. It may have had a better start than the 360, but that's largely due to a stronger launch (the 360 was supply-constrained in its launch holiday, giving it a very weak launch) and big short-term boosts during the holidays due to temporary Black Friday/Christmas price cuts. Essentially, this is a more front-loaded generation than last gen (though not as front-loaded as Gen 5 and earlier were). In terms of market share, it's not even close to the 360, and that's why nobody should have expected the XBO to retain it's lead over the 360.