$0 Earned in 2019 on Employment Gold Card ARC. 2019 Tax Return Needed?

Help! Asking for a friend: My friend is on an Employment Gold Card ARC and worked in 2018 and filed taxes for that 2018 income, but didn’t earn any income in 2019. Do they still need to file taxes for the 2019 year even though they earned $0 that year?

Is he/she living here? Than yes, else no.
But not making money on an Employment Gold Card? He/she needs probably some prove of not making money.

How did they not earn any income in 2019?