APT_ORACLE_LOAD_OPTIONS is used to set PARALLEL to FALSE (Tips)

Say the job is running on 8-node configuration File, then

If you set the sqlldr parallel=false and the stage = true, you will get 8 sessions.
If you set the sqlldr parallel=false and the stage = false, you will get 1 session.
If you set the sqlldr parallel=true and the stage = true, you will get 8 sessions.
If you set the sqlldr parallel=true and the stage = true, you will get 1 sessions.

Sqlldr parallel option has to do with how indexes are maintained, not the parallelism of the stage (sqlldr cannot determine the parallelism of datastage).