He explained what I thought I was hearing: Chopin quoting himself, repeating himself with some variation. Bi-rhythm (what Frederick calls bi-metrical) is one rhythm for the right hand and one for the left hand and almost requires two brains, but, after frequent practice, it starts to happen.
A rondo is an instrumental form characterized by the initial statement and subsequent restatement of a particular melody or section, the various statements of which are separated by contrasting material. This pattern reveals itself in good writing, too.
From Frederick we learn that composers are sensitive, as are writers, to what is happening around them.