That article was written YEARS ago in 2003. Who knows how accurate the result actually is?
BMW chose to build the X3 thru a subcontractor because it was (and still is) running at full capacity. In 2004, they had the new 1-series and 5-series to build in Germany. Thus, it makes more sense to outsource the job, than spend millions in additional capital to expand their own existing infrastructure.
Austria does have lower labour costs than Germany. However, the price of raw materials has steadily risen since then. The Euro is now also worth much more v. the USD than it was back in 2003. There are just too many factors, in addition to the fact that the article was dated back in '04, to determine whether the article is correct.