You could look at the Contact property ‘Record Source’ for this. If the chatbot has generated a new contact, this will show as ‘Conversations’.
Caveats: if you’re using multiple inboxes, this won’t show you which chatbot/inbox has generated the record (you can bypass this with custom reports using the Conversations object), and also won’t be the case if your chatflow is directing users to fill in a form, rather than leave their information with the bot itself. This also won’t show for if existing Contacts interact with the bot, regardless of if the chat has been completed.