When did they start the development of the game? Afaik the downgrade rumour goes as this:
Step 1: In the beginning WiiU had a stronger GPU. The heat generated was too much for the console.
Step 2: The now considerably slower GPU with 160 ALUs @ 400MHz got introduced.
Step 3: A few month bevor release the clockrate of the GPU got upclocked to 550MHz (and the CPU from 1 GHz to 1.25 GHz)
So IF the rumour is true and the developers here got there first devkits during Step 2, they of course only have seen the upgrade.