What does "copy of" mean when doing "delete archivelog"?
Based on the documentation:


  An image copy is an exact copy of a single data file, archived redo
  log file, or control file. Image copies are not stored in an
  RMAN-specific format. They are identical to the results of copying a
  file with operating system commands. RMAN can use image copies during
  RMAN restore and recover operations, and you can also use image copies
  with non-RMAN restore and recovery techniques.


Even the original archivelogs count as copies, as they are a copy of an archived redo log. The 2 statements are equivalent even if you have the same archivelogs 1 or 10 times on the disk. The COMPLETED BEFORE 'SYSDATE - 7' clause will delete archivelogs that are older than 7 days.

This is not true for datafiles however. The original, actual datafiles don't count as copies. If you create a copy of a datafile with the BACKUP AS COPY command, that copy will have the data from the file the time it was copied, and the database will not use that copy, except for recovery procedures. If you switch a datafile to its copy with the SWITCH command, the copy becomes the original, and the former original becomes the copy.