The key point about a site for professionals, from my perspective, is not that each and every question will be about an advanced topic that only those with years of experience can answer; instead, on a site for experts, we should merely expect people to be professionals when they ask their questions.
A question about a relatively trivial concept for experienced programmers is okay as long as the asker attempts to solve the problem, shows research effort, explains where he or she is stuck, and provides the community with a starting point that isn't day 1 minute 1 of Intro to Programming.
To be a professional on a Stack Exchange Q&A site, one only need to ask questions that are serious. In this case, as Rachel says, he's asking about questions he's stuck on, and he's attempting to learn on his own. This is the clear markings of a professional who will one day become an expert.