Backup and sync are separate things in Kanbani.
Sync operates per-board. It can’t modify your global preferences (e.g. Author) but it can merge remote changes so that neither another user’s nor your local data is lost.
Backup is blatant: it knows nothing about boards and cards – it simply sweeps everything (like Titanium Backup but needs no root).
To replicate your device’s Kanbani, do backup.
To bring your colleague up to date – do sync. Doing backup here will discard all of his own boards and changed cards, give access to your private boards and make his new cards signed by yourself.