Answer: When both shows began production, the extraterrestrial main hero was seen by his creators as entirely human and of terrestrial origin.
The idea that Goku and the Doctor were aliens came later on and were retcons. Doctor Who had been on the air for 6 seasons before the term “Time Lord” was ever spoken. Likewise, the reveal that Goku was an alien was greeted with disbelief and shock by Shonen Jump readers at the time (Dragon Ball had been serialized for years before the term “Saiyan” was ever used). True, Goku had a tail (among other oddities) but earthlings in Dragon Ball could have very odd and inexplicable features.
In the case of the Doctor, when the show began production, the backstory for the character, according to internal BBC documents, was that the Doctor and his grand-daughter were refugees who fled backwards in time from a total nuclear war in the 51st Century, one that vaporized the earth and the human species and made the Doctor an exile forever. This background explains why the Doctor, in his original incarnation, was misanthropic and believed that the human species were violent and self-destructive. (It’s also worth noting that according to the initial series concept, the Doctor built the TARDIS himself.)
The earliest episode the Doctor said he was not an earthling was “Inside the Spaceship.” It’s interesting that the Doctor was examined medically at many points in the initial seasons and nothing unusual was ever found. Many Whovians explain this by saying that Time Lords only get a second heart after their first regeneration.
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