No, it was not only Austria going after Serbia, but Austria and Germany together going after all of their neighbours, including Serbia, France, Russia, Belgium, ...

Not until Russia started to mobilize to defend Serbia. Australia versus Serbia would've been a minor conflict if it weren't for the various defensive agreements the Great Powers had with smaller states.

If we were to be pedantic here, Austria was losing badly against Serbia for more then a year. At that time it was clear that Austria did not have a standing chance to win against Serbia in any meaningful way without extensive help from other countries, so the conflict couldn't really be qualified as minor.

The things started to change when German army joined with Austrian forces in attack to Serbia, and Bulgaria decided to step in and stab Serbia from behind, but at this point the conflict was already far from "minor" and "local".