pgsql user (Postgresql)

The port/package should create a postgres user and group:
PG_USER?=       postgres
PG_GROUP?=      postgres
PG_UID?=        770
PostgreSQL's user was changed, this definitely is postgres for PostgreSQL >= 9.6 (pgsql remains for older versions). From /usr/ports/UPDATING:
AFFECTS: users of databases/postgresql96-server

The default unix user used by the PostgreSQL daemon has changed to
`postgres' to reflect the long time upstream's convention. Any scripts
you have using the old `pgsql' unix user should be modified when upgrading to
PostgreSQL version 9.6. Older versions of PostgreSQL will continue using
`pgsql' until their end-of-life.


Your source is simply not up to date. Moreover, this change to the ports tree may not have affected binary packages before a while (especially with a quarterly repository)