BBC intended to clarify this film's place within the Whoniverse.
From the trivia of the fiftieth anniversary episode "The Day of the Doctor":
"Kate's (Kate Stewart of UNIT, daughter of Brigadier Lethbridge-Stewart) line about the disastrous consequences of information about the Doctor getting into the wrong hands was supposed to be juxtaposed with a film poster for the Peter Cushing films - Dr. Who and the Daleks (1965) and Daleks' Invasion Earth 2150 A.D. (1966), implying that they are fictional in-universe. Unfortunately, they were unable to afford the rights."
So this film is simply the annoying result of some hack screen-writer plagiarizing rumors he has heard. The question then becomes, which early Companion was a gossip and spilled the beans. Ian Chesterton seems to me the likely candidate, a bland academic probably trying to find a way to impress women.