Z will mean different things on different airlines. Z on Air Canada is the student fare and the inventory that Airmiles (not Aeroplan) buy their seats from. It is a deeply discounted fare and earns no points on AC.

Either way it sounds like cme10ae bought the seats they wanted and then the system reflected that.

If they were discounted Business Class tickets in this case it would seem logical that they would need to be purchased this far out.