Headcanon #86
Pokemon types are not as simple as they appear to be in video games. Researchers determine a Pokémon’s type based on a variety of factors. This includes battle techniques as well as a Pokémon’s abilities and strengths in battle. Because the first Pokémon partners were used for battles, types are almost strictly determined by a Pokémon’s battle abilities.
The Flying-type you know in the video games doesn’t actually exist in the real world. Flying is more of a technique used in battle (like abilities-think levitation, but they’re flying not levitating). This is why Pokemon that fight while airborne will be immune to ground-type moves and prone to electric-type attacks. On the other hand, Pokemon that fight on the ground, such as Dodrio, do not share the same defenses and vulnerabilities.
Typing Pokemon is much more complex than in the games, and certain type combinations (like fire and rock) can sometimes create combo types, like magma, that act slightly different than the standard type combo. This phenomenon is what makes Pokemon like Magcargo different from Pokemon of the same type Combo like Hisuian Growlithe or Coalossal.