They are a form of industry. Historically, as developed nations moved from an industrial base to what we have today, people left the factory floors and began working in office jobs. These are the "new industries", such as software/legal/financial etc...
While software (and film, music etc) can be classified as industry, legal and financial are not. They do not produce any goods.
We have basic division into 3 sectors:
Industry - producing goods. Every factory, mine, etc would be here.
Agriculture - producing food unprocessed food. So grain, eggs, milk, meat. If it's processed food, it's in industry (like bread, cookies, candies)
Service - provides services. Here we have lawyers, brokers, plumbers etc.
Classifying offices as industry is blatantly wrong. Offices are not supplying commercial, You can't sell advocates service at a store. Software etc, well, ok. But they should usually also require industry, cause with some minor exceptions (like PDS games. Still, most games can be bought as a physical copy) there will always be smth to produce actual product. You need to print the book, burn the CD, You need to produce a cover for that CD.
And since suppplying goods to commercial is an important part of the game the RCI should not take offices as industry.
Offices are industry in the sense that "industry" is more along the lines of "non-service jobs" in Cities
Yeah, the problem is Offices are mostly services.