I don't think that the "De-icing fluid" theory makes any sense. If the event had happen at the begining of the flight, may be, but at the end of something like 1 hour flight, I don't think so.
There seems to be quite a remarkable coincidence in terms of Engines involded in this fume events.
-the B757, which seems to have a "tradition" on the subject, has RR engines. (It is also powered with PW engines but I'm not aware of this engines causing any fume events)
-this Germanwings A319 has IAE engines which, one of the manufactors contributing to this engine is .... RR. (I believe that the IAE also has MTU on it, and this is probably the reason why Germanwings switched from CFM to IAE)
-the A330s of Lufthansa have .... you guess it right .... RR engines.
Wondering if RR is overdoing the lubrication of its engines?