2 Conductor or 4 Conductor Wire CAN Bus

A1) The forum is not able to see what the <...we...> used, nor why it did so.

A2) CAN-bus is covered by ISO 11898.

A3) -

CAN bus is kind of like ethernet. The devices hanging on the bus talk when they can. The four wires are power, ground, and a balanced line, i.e., when one signal goes high, the other goes low and vice-versa.

"...several de facto standards for mechanical implementation have emerged, the most common being the 9-pin D-sub type male connector with the following pin-out:

• pin 2: CAN-Low (CAN−)
• pin 3: GND (Ground)
• pin 7: CAN-High (CAN+)
• pin 9: CAN V+ (Power)"

https://en.wikipedia.org/wiki/CAN_bus

Here is an introduction to CAN bus that might be helpful...

https://www.csselectronics.com/screen/page/simple-intro-to-can-bus/language/en

Low power devices like some sensors can use CAN power. Higher power devices - ECU or motors, etc have their own power supply and power their end of the bus.