yet another step towards higher-resolution displays. There's no mention of pixel pitch, but I assume they're using off-the-shelf projectors for pretty standard results - the high megapixel count comes from using 28 projectors and the massive area!
Interesting application, but the focus here is more on interface/human interaction than on absolute image quality.
They could have used much better full HD projectors had they had the cash and willingness.
The best projectors are now 8K, meaning 8000x4000 pixels or 32 megapixel with a single device.