Why are regular languages called "regular"?
A quick check of the sources reveals that Chomsky called the levels of his hierarchy just “type 0, type 1, type 2, type 3”. He mentions in a footnote that his type 3 corresponds to “regular events” of Kleene. Kleene wrote there: We shall presently describe a class of events which we will call "regular events." (We would welcome any suggestions as to a more descriptive term.)

It would thus appear that the term is a historical accident, and in any case has no bearing on the relation of regular languages to context-free languages.