I got the impression he wasn't working directly on the ad injection software at all. He was working either on different software or in a different division of the company. It sounds like 5oonRed has a culture of not talking about the ad injection and that their internal jargon was designed to disguise it.

He wasn't shocked to find that he personally had been writing an ad injector. He was shocked to find that the company he was working for made such software without his realizing it and that it derived most of its revenue from said software.