If you can find that statement in LASORS I will agree with you.
It would appear that as a PPL you cannot log time 'carrying out the duties of the PIC under the supervision of the pilot in command' as PIC U/S and in order for PIC U/S to be counted towards grant/renewal of a licence (in the case of a pilot holding a higher licence than PPL) in that scenario the aircraft must be a muticrew aircraft.