He was pushed to retirement in 1940 (he was supposed to in 1939), after the Battle of Britain, so he was not in command for the whole war. He was a great commander to his men, but clashed with his superiors and peers. In retirement he was a bit of an eccentric. He subscribed to many outlandish theories and beliefs, such as reincarnation and had visions of dead fighter pilots taking off from mountains of light. Being a good military commander during the Battle of Britain does not make one an expert on future technology. I would take his theories of alien technology with a grain of salt.

Do you have a source for that statement? There's no "Commanding Officer of the Royal Air Force"; the closest thing would be Chief of the Air Staff, and that's not a role Dowding held; he was c-in-c of Fighter Command in 1939, one of a number of Commands working under the Air Council, and was shuffled out of that role in November 1940 before retiring from the RAF completely in 1942, so most certainly would not have been "in charge" in 1947.

That's not to say he wasn't a firm believer in flying saucers (along with spiritualism, about which he wrote books, and fairies, amongst other things) but I would suggest the burden of proof remains on the theory that alien technology accounted for the specified advances.