Why soldiers at Dunkirk thought the RAF was absent

Why did it become common knowledge that the RAF was absent at Dunkirk when it was actually fighting?

Much of the air battle occurred beyond the beach's view, so honest eyewitnesses mistook what they could not see for activity that did not happen.

People naturally describe the battle they can see and hear from their own station. Soldiers on the beach could not observe air combat taking place miles inland, just as merchant sailors might miss escorts fighting U-boats beyond their part of a convoy. In one convoy example, merchant crews condemned their escorts after losing three ships because they had not seen the fighting in which eight U-boats were reportedly sunk. Engine-room crews, bridge teams, and gunnery personnel likewise experience different versions of the same naval action. An eyewitness account therefore needs to be read with the witness's location in mind.