Pi existed long before all of us. Pi is an irrational number that fascinates all scientists and engineers. We use the name Pi-Bot because our robot uses the shape of Pi (the Greek letter). There is no better name for our robot than Pi-Bot.
We are a big fan of Raspberry Pi. However, our Pi-Bit does not use Raspberry Pi. It uses Arduino compatible microcontroller. We realize that there may be some confusion with Raspberry Pi and hence we clearly indicated in our story that Pi-Bot does not use Raspberry Pi.
In our story we show how we arrived at the shape of Pi as the chassis for the robot after optimization analysis. In that sense we have more do with actual Pi than Raspberry Pi. In this context it is also important to remember that Raspberry wanted to use Python (not Pi) originally which later became Pi (instead of Py).