Depends on what you base the percentage on. If it is the global population, then 5% of 7 billion is 350 million. So to be in the top 5% there must be at most 350 million people better than you.
Now consider a niche sport, say Ultimate Frisbee. I would guess that much less than 350 million people even know the rules. So invest an hour to learn the rules and play it a little with your friends. Voila, you are in the top 5%. And that is for an athletic sport.
You are probably talking about 5% of the people actively doing it like being registered in an association. In this case, 50% sounds more realistic to me.
Assuming the potential performance of actively engaged people is roughly normally distributed (even if, as a group, they come from the upper end of the general population on that axis), then I think 50% is too conservative. Nobody can perform above their potential by definition, but lots and lots of people will fail to live up to their potential, making room for their below-average colleagues to outperform them with enough work.
Now consider a niche sport, say Ultimate Frisbee. I would guess that much less than 350 million people even know the rules. So invest an hour to learn the rules and play it a little with your friends. Voila, you are in the top 5%. And that is for an athletic sport.
You are probably talking about 5% of the people actively doing it like being registered in an association. In this case, 50% sounds more realistic to me.