The article is only a few sentences, but it makes it clear that this guy has only been selected for training as part of a study on the feasibility of physically disabled (although he is a Paralympian) people entering the space program. In other words; "THIS IS ONLY A TEST."

A long while ago, I was discussing this very thing with others on reddit. We came to the conclusion that although there was absolutely no perceived limitations for the (say) leg-less astronaut within the spacecraft, it was the possible scenario of escaping a crashed craft in gravity (and the need to be able to help others to do so) that was a large potential drawback compared to a fully-limbed individual.

Also there was the extremely problematic (although a little bit funny in a black humor/ironic way) issue of spacewalking. This was agreed as a much smaller issue, since not all people who go to space need to be able to perform a spacewalk for a given mission.