I believe the Bayern director too, but then € 20 million per year is Christiano Ronaldo territory, almost 400 k pw. Now, what I expect the truth to be, admittedly speculating, is that the reporters have placed the sign on fee as part of the first year salary. Take that 10 m of the top and you've still got close to 200 k pw.
Doesn't matter really what the exact sum is, only matters that I think it very unlikely that he'd get a better deal at Arsenal any time soon.