Yeah he worked in Microsoft before that and when he ended in Nokia the path was quite clear what it would be. But I’ve had the chance to talk with many engineers that were working at Nokia back in the day and the problems didn’t start because of Microsoft.
Basically Nokia had the whole management divided between symbian, maemo, and windows mobile, and as they couldn’t agree on a future path all the efforts were divided. Symbian was quite a disaster at the end and it wouldn’t have gone far most likely, those that wanted to continue with it didn’t have a clear view of the changes coming in the mobile world.
Maemo was great, really advanced, based on Linux, and working really well, maybe too advanced even, specially for your common users back then. The whole system was constantly put down and delayed and the first devices sold wouldn’t even work as a phone, only the 4th ended up with mobile connection, which didn’t help at all to make it useful (wifi was not as big as it is now) and sold.
Finally there was Windows Mobile which was still starting basically then and had far less strength, but with the support of Microsoft behind it it was easier to push it out. I don’t understand why it still has such support when it comes to the UI, I personally never liked it and it felt too simplistic and boring, but the more options the better I guess. Of course once Microsoft managed to plant his own guy inside Nokia they managed to favor the balance towards Win mobile and the other two were left behind more and more.
So Microsoft was a key part in what ended happening but they were not the ones that put Nokia in trouble. That was a lack of direction in the management level.