Of course, my question isn't about the existence of magic. It's about coherence of the story.
Imagine two neighbouring countries. One of them resembles our society – it's science based, no magic, people have what we would consider 'rational' thinking. The society priors education, but they also have developed art, economy, military defense mechanisms, etc.
The second bordering country is completely different. It is a feudal society, with technology set back decades. And in that world, 'magic' exists. The magic ranges in a wide domain. Some people are very powerful, they can use telekinesis on long distance, control weather, control chemical reactions in their bodies, etc. Others are much weaker, they can only manipulate things in a very short radius. Most cannot use magic, but that a minority can is accepted and is seen rather than a virtue than as a fault – so no witch burnings. The majority of the population, even though they cannot perform magic, is in any case passively adapted to its existence – for example, if air temperature drops drastically they would survive for longer than biologically possible, or they can tell whether the water is contaminated by the sight, etc. (I am actually trying to find some sort of sci-fi explanation for this magic, but that is off topic. The actual nature of magic is irrelevant to the question).
My question is, would this scenario be possible? This separation of societies. The two countries are separated by a mountain barrier, so there is no – or close to none – interaction between the folk. Would it be possible for two close countries to have evolved this way, completely isolated from each other and having completely different laws of nature? Would the two populations be considered the same species? They obviously had a common ancestor, so would it be possible for one people to develop the 'magic' ability without the other one doing so?