I had a similar situation where a TA booked me AC/AC/Delta/Delta/AC for a two city tour. The Delta flights appeared in the Flight Booking as AC whatever. The airplane types were correct (and they were not planes AC uses.) There appeared to be no consequences of this whatsoever: I was able to upgrade the AC leg, to web checkin the leaving-Canada-on-AC leg, and so on.

The presence of the letters AC on the screen is undoubtedly an artifact caused by a web programmer pumping out AC followed by the flight number instead of writing to code to see what airline the flight is with. Don't interpret it as any more than that.