Forget the terms sinking and sourcing. They have been butchered to the point of being arbitrary.
Maybe an easier way to look at it as Bob mentions
N for Negative Logic and P for Positive logic.
The key is to look at what the field device gives you in the ON state. Think of it as a wall switch in your house.
An NPN wall switch would give you common (connects you to white)
A PNP wall switch would give you HOT (connects you to the black)
In either case, when the switch is off you have no current path.
So the in the NPN analogy of wiring a 115vac light bulb, you would bring 115vac to the bulb all the time, and switch it the common.
With the PNP analogy, it would be just like it is normally done. Common is brought to the bulb all the time, and you switch 115vac to it instead.
Applying the same reasoning to a DC photoeye
NPN ON:0V
NPN OFF: N/C
PNP ON: +V
PNP OFF: N/C