Not sure if I should believe that 10% of the gaming market are tablets. As far as I know tablets are a dying breed. According to this prognosis it's going to grow by 18% in the next 3 years? While the PC market will stagnate/shrink?

As already pointed out, the title is wrong.

They are predicting the following changes in revenue for 2020 (roughly):

Consoles: +11%

PC: -6%

Tablets: +27%

Smartphones: +75%

I'm not that sure that tablets are dying. They are surely being outperformed by smartphones, so we can see that their forecast is way less optimistic. The growth in consoles is probably on par with what we're regularly seeing. PC shrinking is the big question mark. Most of these revenue is for F2P games. Maybe they are thinking that mobile can steal some of that crowd? Or the general decrease in the PC market may increase the price of parts, since a lot of stuff isn't exclusive to gaming PCs (the only growing segment).