The question of what did this bochur gained from having been to Israel when he’s subsequently observed viewing inappropriate material is an odd question.
Since there’s no way for us to know what spiritual level this young man was on prior to his visit, similarly there’s no way to assess what positive influence his visit to Israel had on him.
Perhaps the better question to ponder is what improvements we can make in our own lives and the lives of those who learn from our behaviors to counteract the negative influences around us.