Immediate family members of PR and Citizens don’t need authorization that is what I was referring to. Your parents need an approved visa and authorization. Their refusal states that officers don’t think a visit is essential at this time due to Covid. This also is because you are temporary workers and don’t have the same “benefits” as the parents of PRs. They can apply again but need strong profile to show funds, short visit, ties to home country but given the reason for their refusal, they may need to reapply when travel restrictions ease.