Can anyone tell me the major difference between cold backup and cold cloning?
There is no comparison of difference, since they are different thing.
Cold Backup is a safe copy of existing database dismounted (i.e offline mode). The RMAN generated a new file which is read/write only by RMAN, also RMAN can generate a copy of database files on specific location.
Cloud Cloning is a duplication of existing database with was backed up in offline mode. The RMAN restore database files which is read/write by a Instance.