It's hard to comprehend at first, but I have a few theories:
1. Digital Sales
There has been quite a few sales on Ubisoft games on the PC in the past few months, which means that more people will be paying money to buy copies of their games. This is good news for people of my second point, because...
2. People waited for broken games to be fixed
Let's be honest, most AAA Ubisoft games released had some sort of issues in the past, which cause many lost sales at the release of these games. It's the reason why Ubisoft never revealed or trumpeted the sales numbers of the various games it's released in the financial year. But, they have been fixing it, and even though people have been reluctant to buy them at first, seeing Ubisoft fixing the PC related issues of games on sale meant that more than expected sales figures were realised.
3. Revenue vs Sales
It's very possible that the figures that's being reported are profits made from the sales of the various games, which means that most revenue lost on games sold on the consoles will go to the various licensing costs to Sony and Microsoft. With the uptake in PC sales, it meant that Ubisoft had a bigger share of the revenue from each sale, thus it is possible that they still made more money from PC sales even though it's not necessary that the PC actual sales numbers may be higher. The margin of profit is higher though, which means more revenue to Ubisoft.