PIP descision and SSP

is it true that DWP regard not working and on SSP - as short term sickness .My sons decision letter  amongst other things stated due to level of his intelligence, compentance plus he obtained a degree 4 years ago he is regarded as compatent and physically able for many descriptors which has not been the case for almost 6 months when he last worked .It has been suggested to me maybe ESA would be better but this cannot be obtained until SSP ends.