NPRs do not build PDCs, only player does. The NPR probably has small Orbital Weapon Platforms that you haven't seen yet. Which is kinda weird because usually their OWPs are huge.
Couple of problems:
1) I am detecting *no* active sensors of any kind. Have no clue how they are even able to target me with an OWP.
2) The planet is 11.2m km away which should be in range of my "Active Search Sensor MR23-R4 (1) GPS 768 Range 23.0m km Resolution 4". If I've read things correctly, this sensor should detect everything larger than 200 tons & closer than 23m km. If its a OWP, it would have to be 2500 tons at a minimum to be launching 43 size 1 missiles at me every 5 seconds based on my calculations.