Yes, the MacBook was released April 10, but the Chromebook Pixel was already shipping USB type-C in March. Someone in the other Thunderbolt type-C thread also mistakenly claimed that Apple was the first company to use type-C.
I believe the MacBook was technically the first USB-C device announced (and rumors about it go all the way back to last year), but the Pixel shipped earlier.
It's not a big deal. No doubt both products were being developed long before they were announced, so Apple and Google were both ready to be the early adopter.
Now I'm just waiting for something to connect to the Pixel via a Type C <-> Type C connector, other than another Pixel ;)