The bot has a number of learning settings, which you can see on botlibre.com in the bot's "Learning & Settings" page in its Admin Console.
When learning is enabled as "everyone" then the bot will learn new responses from the users it chats with, or the conversations in imports or listens to.
Synthesis can be enabled as the bot's default response, if it has no default response and synthesis is enabled. In order for synthesis to work you must also enable "learn grammar".
Synthesis will generate randomized "gibberish" sentences base on the words and sentences it has learned.