First...There is no such animal 'passive radar'. I do not care how many popular media sources you or any other Iranian bring on that uses the phrase 'passive radar'. Radar detection is a two-parts process: Transmit and Receive.
Transmit is 'active'. Receive is 'passive'. Without either one, you have no radar detection. I have many times educated people here on the technical aspects of radar detection, complete with non-disputable sources as to this 'passive radar' nonsense. Smarter people than you have stopped using that phrase. What you are talking about is properly call a 'bi-static' radar configuration and there is nothing new about that.
Receivers A and B are 'passive' detectors and this is the source of the misunderstanding about 'passive radar'. I suggest you use the keyword search feature and learn something.
Second...Assuming the generosity that Iran did detect the RQ drone via that 'passive radar' system, that does not mean the system will be effective against combat aircrafts. The UAV does not have countermeasures. Combat aircrafts do. In that bi-static radar system, the Transmitter must be continuously active in order for the entire system to work. Take out the Transmitter and the entire system collapses. That is the main weakness of the bi-static radar system.
Third...Assuming the generosity that Iran does possess the American UAV and not just some model hacked up, everything you said about how Iran came to its possession is: pure assumption.