Is it common to talk to KCRQ that far south, rather than SCA?
Especially when just flying between KMYF and KCRQ a lot of pilots around here won't bother with flight following. KCRQ can get rather busy sometimes, and I sometimes call the tower up to 5nmi from the class D boundary just in case if I'm not talking to Socal.
It looks like he went down near the Del Mar racetracks (VPSRT) which is ~6nmi from the class D boundary, so I don't think it's unreasonable for him to have been on KCRQ tower at the time. Another possibility is he was self-announcing on 122.75 with KCRQ tower as his standby frequency, and probably thought KCRQ tower would be more useful than a few random pilots on 122.75.