One of the features of Telegram is the possibility to do a “secret chat”. The only thing secret about these chats is that they are not stored on the Telegram servers. The data is normally saved in the SQLite database.
Wim and Peter are sending messages to each other. In this case, Peter is the owner of the phone. The messages comming from Wim seems to have a negative Docid, while messages sent by Peter seem to have a “normal” Docid. Both have a “long” Docid in this “secret chat”, while other chats seem to have normal ascending order numbers.