Maybe he's just reminding that aircraft to report downwind because it's a requirement operating in an MF?
Maybe he missed the last 3 required calls and someone's waiting to go?
And in the case if Grande Prairie - it is a class 'E' control zone.
In case a brush up on RAC is in order for some in this thread..
https://www.tc.gc.ca/eng/civilaviati...-menu-3092.htm