Sorry if I didn't explain the 1861 clearly. He was just visiting the Parrys on census night - we have no idea if it was just that night or a longer visit, or if they were friends, relations, or to do with his training. And, as has been explained, unm is just short for unmarried.
If the earliest record you have for him is in 1862, then that gives a small window for when he emigrated. 1861 census was taken the night of 7th/8th April 1851, so it will be after that and before the first date in 1862 that you have a record of him in Australia.