Obviously, Russia has been maintaining influence (and that is putting it lightly) within Georgian borders. The country has been bullying Georgia, angry that it has become an independent country of sorts.
Georgia, a re-newed country with an urgent sense of nationalism, has been trying to rid itself of any Russsian loyalties and influence. With a cease fire in effect, the Georgian military did a surprise attack (or raid) upon rebels within its own lands.
With the U.S. charging into Iraq to protect its own interests, why should it be surprising that Russia choses to exercise the same discretion?