The purpose of the legislation is to provide the boundaries for enforcement which understandably would be any area within the aerodrome where a pilot, student pilot etc may be reasonably expected to partake in direct/indirect aviation related activities.
Legislation, at least in QLD, exists providing for an offence of being in charge of a motor vehicle whilst under the influence of liquor or over the legislated breath alcohol concentration. To prove the offence, case law exists where the effected person must be directly in a position to influence the controlling mechanisms of the vehicle. The legislation described here sounds like it is along the same lines. Unless there is a specific statute relating to being over the prescribed limit within the grounds, you really don't have to worry about anything if you're not acting as pilot, student etc.
Don't make too much out of this because put it this way, if someone from CASA came in and breath tested you in the club house at a function and decided to send you to court, the matter would be tossed straight out. If however you're sitting in your mates plane doing some engine run-ups at 10pm with a stubby in your hand in the pilots seat, you should be a little worried.