Not a mutant player but how is it possible?

[Altiplano]

This ?



I'm at level 23, in my asso group there are friends at level 27, but I can't buy their players...

You can buy their 1 star players! And you can see what the selling manager cannot. Where the manager 4 levels above you sees some skills at 1% for his player, you will see them with an extra 80%.
Welcome to the world of downselling.
Of course it could be upselling, or hundreds of frendlies.