I suspect he wanted to make absolutely sure you did not think you had been cleared into CAS. On your other point, if you were under a basic service then you were not (“I wished to hold onto my Radar Service”) on a radar service and you were not under radar control, ( “but did not return to Radar Control”). Basic service is as the name suggests, basic, even if you are given a squawk do not assume you are identified and do not assume ATC will notice if something bad is about to happen.
Rod1