This is not necessarily true. My wife, who worked both part and full-time, could get these even with a part-time job. If they wanted only those employed full time, I think they would have said it already. But we'll see.
If that was the case shouldn't they also mention that current students could apply. Why would they ask for graduates? As u see they mentioned the certificate should be awarded.
"Have been granted one of the following credentials, following the completion of a program study from an eligible institution as defined in a): "