I think instead we should just say
> Rails, like most libraries, uses the `private` keyword from Ruby for defining internal API. However, public API follows a slightly different convention.

Which leads into:
> Instead of assuming all public methods are designed for user consumption, Rails uses the `:nodoc:` directive to annotate these methods as internal API.

Previously written as:
> Instead of making all Internal-API private, Rails uses the `:nodoc:` directive for non-user-facing API.