Found vapes in my 15 year old's bag. Handled it badly. What now?

I was looking for his hostel form and found two vapes and a packet of flavour pods. I did not wait. I confronted him the moment he came home, in front of his grandmother, and it turned into shouting on both sides. He has not spoken to me in three days. I know what I should have done. Stayed calm, asked questions, picked the moment. I did the opposite because I panicked. I am an HR head. I handle difficult conversations for a living and I could not handle this one. Parents who have been here: how did you reopen the conversation after getting it wrong the first time? And realistically, is vaping at 15 the emergency I am treating it as, or am I making it worse by treating it that way?