Speculating on his country of origin based on his age (btw 30 and 35) and iterant nature of his jobs:
Working holiday visa 417 is the most likely: on this visa citizens of Canada, Denmark, France, Ireland, Italy and UK are allowed up to age 35. Citizens of other eligible countries must be 30 or below when applying for the visa.
If he held this visa in 2019, he could have stayed up to 3 years if he met further eligibility requirements.
In 2019 he was only 28 so there was a longer list of eligible countries including four Asian countries: Hong Kong, Japan, South Korea and Taiwan.
Second possibility is working holiday visa 462 which allows up to age 30 citizens of (among others) China, Indonesia, Malaysia, Mongolia, Singapore, Thailand and Vietnam.