Can anybody help me out here involving what my friends friend took from my grinder and should I be mad?

So I have been a smoker for about 6 months and I am currently a freshman in high school, (was pressured into smoking and kept doing it) Anyway I had a friend come over to my apartment yesterday with another friend of his and we had a sesh. They brought about 4-5 grams of some medical grade cannabis and somehow forgot to bring a grinder. I have had my grinder for about 5 and a half months (I have probally grinded up close to an ounce) and up until now never really noticed that there was a 4th capsule at the bottom that you have to unscrew to get to. Now before you ask how I didn't notice, the part on the bottom is VERY VERY small and (I'm talking maybe to US quarter widths) the screen on top is VERY well made and it is also so tight I never figured some stuff can fall threw it, as well as why the 3rd part of the grinder was so lengthy compared to the new found 4th chamber. Anyway my friend went to use the restroom and his friend began to talk up a conversation while grinding up his weed. When he was finished I began to see him start to unscrew the bottom and I see mounds of this powdery looking stuff fall out of it. I looked at his face and he looked really surprised yet he still scooped all of it up and threw it into his jar with all the rest of the weed. I know I probably should have asked what exactly he just took but I was already stuck from a couple depression pills I have took just a couple hours before. Anyway we smoke and my closer friend gets super zoned out and unresponsive so I figure why not ask his buddy what exactly he took. Well he didn't really give me an answer and decided it was his time to leave and he would be back for my friend later tonight. So I am wondering what the hell just happened?