It's interesting to see him acknowledge directly that his personal familiarity with Microsoft played a role in the decision (at about 1:00 in). But aside from that, well... opinions differ. At about 3:15, he said that the danger if they went with Android is:
1) The platform would succeed.
2) They'd be one among a crowd of Android phone manufacturers.
3) It would be hard to differentiate from the others.
Contrast that to Windows Phone 7, where:
1) The platform is playing catch-up, and may fail entirely.
2) They're already one among a crowd of Windows Phone manufacturers, with LG, Samsung and HTC already shipping, and Dell having devices in the pipeline.
3) The party that controls the platform has chosen not to allow differentiation, requiring all the devices to be lookalikes[1].
On all his supposed drawbacks of Android, WP7 looks even worse.
There's some other odd stuff in the video, which begs for explanation. He starts by saying that "Microsoft has placed a large bet on us." But it isn't yet obvious why Microsoft has bet more on Nokia's success than it has on the success of the other WP7 handset manufacturers. And if they have, I can't imagine HTC or Samsung being happy about it.
There's also some stuff at about 2:30 about how each party has licensed technology from the other, with an implication (though not an outright statement) that money might be flowing both ways. If that's true, it raises the possibility that the sale of an HTC WP7 handset results in royalty payments to Nokia, for the mapping technology that Microsoft has licensed. That could cause real friction with the other vendors.
(To clarify: the mapping technology bit was part of the announcement, though it wasn't clear what it was doing there; the payment structures were not announced, but Elop did seem to imply in that video that money would be going both ways, and I'm not sure what other reason there is that Microsoft would have to write checks to Nokia.)
[1] http://mobilementalism.com/2011/02/12/the-photo-the-nokia-fa... has a photo (second in the post) with a bunch of them. They all really do look alike.