Positive discrimination in UK civil service roles (similar to the BBC) means that if two or more candidates score THE EXACT SAME in an interview/application you can pick the person with more protected characterstics to ensure a more diverse work place.

It is not used to hire less talented or skilled individuals.

Source: Been a hiring manager for such an organisation.

What's actually happened is that the BBC are hiring for multiple trainees and have ringfenced a position for a minority person because as they mentioned, they've struggled to actually hire minorities in that role before. A trainee role literally requires fuck all skill so it's not like they're going to be missing out on some white savant that should be in the position instead. It's to promote the role to people who may not even try to apply to it because they think they won't get it because of how white they perceive the organisation to be.