I don't know what they need so many GPUs for. There's 16 displays inside, and the sphere itself has fewer pixels than even 1 of the internal displays. You could probably run the sphere off a laptop if you aren't trying to do anything fancy.
Maybe they plan on doing crazy live simulations on it or something. I can't imagine what kind of displayed image would actually use all 150 of them. Nvidia A6000 cards are damn powerful.
It does seem suspiciously like they picked 150 completely arbitrarily to make the project sound impressive, when they could have easily done it with 20. I'm sure a bunch of people in the middle made a bunch of money off that transaction too. Or like you said, maybe this is Nvidia doing some guerrilla marketing