Also, didn't early Arduino heavily borrow from another open-source project, "Processing"?

Processing was/is graphics-centered, so that's where Arduino's term "sketch" come from, if you ever wondered.

https://en.wikipedia.org/wiki/File:Processing_screen_shot.pn...

https://en.wikipedia.org/wiki/File:Arduino_IDE_-_Blink.png

"Wiring", which constitutes Arduino's primary API surface, was taken wholesale from Hernando Barragán's 2003 master's thesis project. It was a fork of processing for microcontrollers and was not written by the Arduino team: Massimo Banzi, David Cuartielles, David Mellis, Gianluca Martino, and Tom Igo.