Light plane pilot reported a conflict with another aircraft in cruise in SCT airspace.

Narrative

While cruising on V186 near ZISDI and PURMS; I received a traffic alert on my Garmin GTN 750txi system. Northwest-bound traffic was at the same altitude and closing fast. I was under VFR flight following but received no notification of the traffic. It also seemed that the controller was confused as to who was the conflicting traffic. I believe I heard the opposing traffic receive a conflict notice for a [aircraft type Y] but we were a [aircraft type X]. When I had a visual on the traffic; they appeared to be deviating left of their course so I deviated left of my course as well to increase the distance between our aircraft. We both commented on frequency 'that was close'.The opposite direction traffic was talking to SoCal so I do not know why they were on an inappropriate VFR altitude. Compounding the problem SoCal did not have a good grasp on the current situation regarding tail numbers; aircraft type; and their position.After this encounter; our last SoCal controller coming into KMYF seemed to be having a 'rough day;' they were using incorrect phraseology such as 'NO' and 'I'm not going to ask again' (not directed at our flight). I'm concerned that there is a systemic problem with the SoCal TRACON.