However in this case, it happened on their continuous integration server -- which probably does more than just "rake test". On our hudson scripts, it does something like "rake db:reset" because some concurrent scripts require data to be persisted in the database and not rolled-back per test.

So when it's running something like "rake db:reset", which simply recreates all tables & seeds the database, it just looks at your environment and assumes you know what you're doing. Hudson (and other continuous integration systems) are pretty automated so unless it prompted you, it would run the db scripts quietly.