You were told wrong.

In fact, the DT file you refer to isn't 'Van Diemen's Land' (Roud 519, Laws L18) at all, but 'Young Henry the Poacher' (Roud 221) with the first two verses omitted. There are close similarities with 'Van Diemen's Land', though (one was a re-write of the other) and such confusion isn't uncommon; but they should be treated as two distinct, though closely related, songs. The refrain belongs to 'Young Henry the Poacher', not to 'Van Diemen's Land'.

Since the DT file neglects to identify any source, it would take more time than I have spare just now to find out if the words there derive from tradition or not; but they are substantially as found on broadsides and in oral currency, refrain included.