To learn what init system your linux box uses, you can do sudo stat /proc/1/exe, since init always runs with pid 1.

The ansible service module is an abstraction over the underlying OS’s default init system. It’s systemd on Ubuntu 16.10 “Yaketty” (but upstart on 16.04 “Xenial”)

Similarly, package is an abstraction over package managers, apt on Ubuntu but yum on Fedora. Each of these abstractions allow users to write more generic code, at the loss of more specific functionality that their OS specific counterparts provide(There are apt and yum modules, for example).