Can Seriously Stressing Already Shy Fish In A Tank Make Them Sick Enough To Die In Only A Few Hours?

My sister has been fighting to have a healthy tank for months and it seemed that she'd finally succeeded because her fish had been healthy for a couple months. Then our uncle who is a total A** H*** terrified the already shy fish by hitting and rubbing the tank while they went crazy on one of his visits. Within hours the shyest fish showed signs of ick and died and the others have been dying off more slowly but steadily since then. My sister in tears has decided it's not worth it and plans to sell the tank when the rest of the fish die. Before I accuse my uncle I want to find out if you think it was totally cirstantial or if you think he could have caused this.