I think it's useful to replace "AI" with "app" any time you encounter it in the wild. AI is a set of computational techniques that is very broad. The problem with considering "the AI" or "an AI" is that people have in mind some kind of AI agent and that isn't really the case.
AI is also not well defined - day one of my AI course in university opened with "What is AI?" Generally once we figure out how to do something using a computer, we decide that's not really intelligent anymore so the implementation isn't AI. An example of that is the minimax algorithm - it's featured "AI: A Modern Approach"[0] but it isn't really something people think of when they hear "an AI".