It says in the Wikipedia fire drill article that in New Zealand schools must have a fire drill at least once every 6 months and that an unplanned alarm activation does not count as a fire drill.
Well, this is correct. An unplanned evacuation is by definition not a fire drill, however in many jurisdictions if an unplanned evacuation occurs it can replace one of the required fire drills. The same practice is gotten from unplanned evacuations.
The school I work at had an evacuation last February due to a faulty duct detector and was no longer required to conduct a fire drill for that month.