TEMP Tablespace Removal
The alert log will show what user added a data file to your DR tablespace, but most likely they logged on as SYS / AS SYSDBA instead of a user that has SYSDBA privileges (one more reason to assign roles to users, especially DBAs.  The alert log is usually in $ORACLE_BASE/diag/${ORACLE_UNIQ_NAME}/${ORACLE_SID}/trace/alert_${ORACLE_SID} (I may have those ORACLE_UNIQ_NAME and ORACLE_SID backwards).

To clean up the DR TEMP tablespace, just create a new TEMP tablespace TEMP2, alter the database to use the new temporaray tablespace, drop the old TEMP tablespace, then rename the new temp tablespace TEMP2 to TEMP:

create temporary tablespace temp2
  tempfile '/some_dir_path/temp2_01.dbf' size 30g,
  tempfile '/some_dir_path/temp2_02.dbf' size 30g,
  tempfile '/some_dir_path/temp2_03.dbf' size 30g
;

alter database default temporary tablespace temp2;

drop tablespace temp including contents and datafiles;

alter tablespace temp2 rename to temp;