The general form of Patrick's point is that the BLS employment statistics don't always map to our common-sense understanding of terms like "engineering" or "software" jobs. So if you want to really understand what's going on, you have to dig into the definitions and how the data is gathered.

An example that received some discussion on HN last year was the employment numbers for the movie industry. Since many (most?) people who work on movies are technically independent contractors working under contract, they are not "employees" and therefore not included in some measures of film industry "employment".