The author never judges whether someone is a valid software developer or not. He ASKS why people who work as software developers don't know the answer to (in his opinion) basic questions. Obviously, you would have to read the whole sentence and not just a part of it to understand the question asked here. For your convenience:

"If you can't answer the majority of the questions on these four papers, and you're working or intend to work as a software developer, you should ask yourself why — most likely you're either you're missing something you really should know, or you're lucky enough to be working within a narrow area where your deficit doesn't matter."