What version does GP report itself as if you do "SELECT version()"?
PostgreSQL 8.2.15 (Greenplum Database 4.3.6.1 build 2) on x86_64-unknown-linux-gnu, compiled by GCC gcc (GCC) 4.4.2 compiled on Oct 1 2015 15:14:22
It was originally forked from PostgreSQL 8.2.15 but they have backported and/or developed many of the features of newer versions in parallel (no pun intended), including protocol and system table changes used by modern drivers and client tools like pgAdmin.
