Data duplication when moving datafiles from one server to another.

Good evening.

Yesterday we experienced some data duplication in several database tables after one sysadmin decided to test in a production environment an rsync script in order to migrate a database from one server to another one.
Postgresql (8.2) was running in source server and rsync script was launched from second one. Second one server had a one day old copy of the same database. Rsync script create a datafile replica in destination server.
Our sysadmin swear he didn't launch the script in a reverse way (that is, from destination to source)... so my question is
How this data duplication could happen? Due to an rsync lock in checkpoint segment or transaction logs? Or he has mistaken source with destination server?

Thans in advance.