[Fizzlemizz]

The mixin created the method on the frame ie.

function frame:OnEvent(self, event, ...)
-- OnEvent code
end

the xml frames OnEvent <Script> tag tells it to use the frame method.

What I posted replaces the mixin method that gets applied to the frame with your new one ie. it just overrides the old function with the new.

PVPMatchResults:OnEvent("PVP_MATCH_COMPLETE")

That's directly calling the method applied (copied) to the frame by the mixin (the one that is overwritten by the code in my original reply).

PVPMatchResults:GetScript("OnEvent")(PVPMatchResults, "PVP_MATCH_COMPLETE")

Call the function currently assigned to the script.