After the banquet.
Harry was asked to go to his bedroom in line with an elder sister who claimed to be a prefect.
At this time, his heart was even heavier than when he just sat down.
Because someone around him told him that the guy he beat was called Malfoy, a member of a pure blood family, and Malfoy's family were all Slytherins.
Very powerful.
Although it sounds funny that a group of 11 or 12 year old kids talk about power and money, it's no surprise that Slytherin is a gathering place of careerists.
The key point is that Harry is now worried about his people