They showed Max and the Magic Marker:
And the guys at Press Play said they ported the code to XNA, they didn’t use Unity.
Windows 7 Phone uses .NET managed code as it’s lowest possible layer. This makes a Unity port extremely difficult. Unity may have C# as a scripting layer, but there is a lot of C/C++ running under the hood that would need to be torn out (basically the entire engine core). I wouldn’t wait on it.
But on the bright side, I think the quality of XNA engine layers are going to improve significantly from this :).
first, XNA would need to be an engine which it isn’t 
Its an API
And for the API its doubtfull, it didn’t raise in quality significantly through xna on windows, xna on xbox and xna on zune either and the zune required a more performant and solid api than the w7 phones that have more power to compensate for “crap”
it is pretty solid and easy to use compared to DirectX and XNA 3 and 4 got it quite a bit forward but its long term stability recently has suffered quite a bit too
I love XNA when compared to Obj-C and the Apple APIs. It’s a whole different animal than Unity though…
Given that, I would like to see a Win 7 Mobile Unity compile. 