What they saw was what got through the RAF cordon. The RAF's main task was to protect the ships from the bombers (still based in Germany at the time) not to prevent strafing of the beaches. That is a job for ground based anti-aircraft weapons. If the other 240 aircraft had got through most of the ships would have been sunk and Britain may have had to capitulate.
During the nine days from May 26 through June 3, the RAF lost 177 aircraft destroyed or damaged; the Germans lost 240.{63} For much of the Luftwaffe, Dunkirk came as a nasty shock. Fliegerkorps II reported in its war diary that it lost more aircraft on the 27th attacking the evacuation than it had lost in the previous ten days of the campaign.{63}
{63}"Einsatz des II.Fliegerkorps bei Dankirchen am 27.5.40.: Schwerer Tag des II.Fliegerkorps," AFSHRC: K 113 .306-3, v.3.