Yes, it all makes perfect sense now! Pies are circular and Pi is often referred as the circular constant. No need to dig further, this has to be the truth.
Edit: Before I get another email telling me I’m an idiot for posting this *sigh* , here’s a quick explanation of the true origin of the symbol:
The Greek letter ?, often spelled out pi in text, was adopted for the number from the Greek word for perimeter “??????????”, first by William Jones in 1707, and popularized by Leonhard Euler in 1737. The constant is occasionally also referred to as the circular constant, Archimedes’ constant (not to be confused with an Archimedes number), or Ludolph’s number (from a German mathematician whose efforts to calculate more of its digits became famous). Source: Wikipedia