If my brother knows that I work in a certain mainstream Yeshiva and I tell him there was a boy that was caught doing drugs in Yeshiva today and do not mention the kids name. Is that Lashon hara even though I don’t say his name as I am casting the Yeshiva in a negative way
Speaking Lashon Hara about a group of people is forbidden, e.g. to speak negatively about the inhabitants of a city or a yeshiva. Therefore, if through your story the yeshiva will be cast in a bad light, it is prohibited.
All the best
Chofetz Chaim 10:12.