Answer:
An arduino is just a micro controller. It has a programmable CPU and a memory storage. There're plenty of other microcontrollers out there that does the same thing like the NodeMCU or the Teensy 3. A quick google search should reveal alot more alternatives.
You can pretty much program the arduino using any language. The only thing is that had someone made a compiler to translate the code into the 1's and 0's that can be read by the arduino yet.
As for manufacturing, I think they use their own custom made controller. I haven't seen a company that used an arduino yet.