Bot cannot detect private messages
The bot cannot detect private messages because they don't really exist in Matrix. A 1 on 1 chat is just a room with two people. As a result, the bot mistakes private messages for group chats.
Relevant code: https://github.com/errbotio/errbot/blob/master/errbot/backends/base.py#L397
Not sure the best way to fix this, could 'fake' it with an object that is both a person and room or create a subtype of Message for matrix messages.