10M (nowadays 16.8M) is the total number of matrix IDs we can see from matrix.org based on phone-home stats from Synapse. 2M (nowadays 5.18M) is the total numb

10M (nowadays 16.8M) is the total number of matrix IDs we can see from matrix.org based on phone-home stats from Synapse. 2M (nowadays 5.18M) is the total number of matrix rooms from Synapse. The ratio is about what we'd expect - there's a mix of DMs, private rooms, and massive public rooms; the DMs will dominate, hence this ratio. Every conversation in Matrix happens in a "room" (even DMs), under the hood, which might be the point of confusion here.