When the Windows Phone decision was done, the smart phone unit was worth much more than what they later got from Microsoft. So no, this explanation does not make any sense.
Nokia clearly had some problems, but it was nowhere that bad. First, Symbian was not as bad as people claim. Second, when Elop announced the switch and accidentally killed Symbian at the same time (by declaring it obsolete), the smartphone unit was still highly profitable and selling more phones than everybody else and even growing faster in absolute numbers than everybody else - with Symbian phones (people seem to believe that it was already collapsing - this is not true). Finally, there was a perfectly fine strategy to transition developers from Symbian to Meego using Qt as a common platform. And Meego was ready at that time as the excellent N9 showed which was released only a few months later. This was a strategy which made perfect sense at that time. Keep in mind Nokia was the clear market leader at that time - Android was nowhere as big as it is now.
In contrast, switching to a Windows which was already failing on the market (Microsoft had 15% market share with Windows Mobile but at that time maybe 3%), a system which was controlled by Microsoft and allowed almost no differentiating by Nokia itself. It also alienated all existing developers, the sales channels, the carriers, and their own employees. The decision was pure madness. Of course, this was entirely to be expected from Elop: