I think you need to ask him for your own peace of mind. There is probably a very innocent explanation but for your own safety you need to check, as it would be a major red flag if he is claiming to be a member of a professional association but isn't.

Incidentally, my own therapist is not a member of the UKCP or BACP which is worrying me now after reading this thread! He is a member of the NCP (National Council of Psychotherapists). Does anyone know if this is a reputable body? Thanks