A large purchase of Samsung OLED displays would be a much more sensible move than an investment in manufacturing for a display tech which may not be around for long.
One explanation could be of necessity. Perhaps Google initially wanted to make a large purchase of Samsung or LG OLEDs, but neither may have the production capacity to fulfill the order. Samsung is already making 70-92 million OLED displays for a recent Apple order, and LG probably doesn't have the needed production capacity that Samsung already has at scale.