Nobody ever said otherwise. The point is Coanda is being used to start the downward motion of the plume. The downwash then helps to direct the plume further downward. End of story.
If we would want to think that Coanda is indeed playing a bigger role here, I would reckon that the downwash first directs the plume downward, then Coanda takes effect to attach to the bodywork, as raymondu, shamikaze and I have said earlier.
Nando, I think the the exhaust gases don't travel at 360kph all the way, as said earlier, it quickly decelerates as it expands. Added to the fast downwash, IMHO it's not that hard to believe that the exhaust plume is indeed being pushed downwards by Coanda and downwash.