This is an issue of dispute whether the thigh is an Awrah or not.

The most authentic opinion is that it is an Awrah and it must be covered at all times.

He wears proper dress , when he performs prayer and after finishing the prayers , he wears short pent ( which does not cover the awrah). This guy claims there is no problem if I wear such kind of dress unless I do not go in Masjid with such kind of dresses