Different people use the word “atheist” to mean different things, so if somebody identifies as an atheist then, yeah, some interrogation may be needed to establish exactly what that person’s self-identification means. Personally, I’m comfortable with the idea that someone who lacks any belief anything that could meaningfully be called a god or gods is an “atheist”. If you want to go further and express a conviction that no god or gods exist, or can exist, or something of the kind, you don’t necessarily express that simply by identifying as an atheist.
In terms of labelling velomont’s position, “atheist” and “agnostic” are not terribly helpful terms, though. All they can do is point to something that velomont doesn’t believe, whereas a label, to be of much use, has to point to what he does believe.
What does he believe?
From his first paragraph, it seems he’s only open to beliefs that are “explicable by the scientific method”. That suggests not only a faith in the validity of the scientific method and the axioms or assumptions that underpin it, but a dismissal of, or lack of faith in, alternative epistemologies. “Scientism” might be a useful label for that except that, as Riemann points out, it has acquired (has always had?) pejorative overtones, and I don’t think velomont is looking for pejorative labels for his position.
From his second paragraph, he doesn’t think “purposes” are given but that they are chosen. This is entirely consistent with his first paragraph. He goes on to suggest, though, the purpose which we ought to choose (“understanding how everything works”) which I think implies (a) choosing a purpose is in some way valuable or worthwhile, and (b) he has either an explicit or an implicit set of criteria against which a particular purpose can be assessed. (Otherwise, how can we say which purposes ought to be chosen and which ought not?) But I don’t think he says enough here about why choosing a purpose is good at all, or about why some purposes are good and others not, to enable us to try and label his position in any meaningful way.
And finally, his third paragraph, which as I have already suggested points to materialism.