Why write in this dismissive tone? Regardless of your personal situation, it would be hard to believe you don't share the common knowledge that virtually everybody uses auto-complete to some degree, e.g. to remember, discover, or abbreviate type/instance methods, argument lists, etc. And why is "API" in quotes? It's very normal to refer to interfaces in languages/platforms as APIs (e.g. "JavaScript's Date API").

Regardless, whether or not a person uses autocomplete for this API is irrelevant - in this case it would be anybody using numbers for things outside this API, and maximally it would be the whole platform if this design pattern is not unique to this API. I.e. the simplicity of this one API has no bearing on the question.