In classical Greece (especially the late 5th century BC and the first 75 years of the 4th century BC), there would have been no distinction between a philosophical achievement and a mathematical one. The same goes for a "scientific" achievement (such as a discovery about the natural world). Every single major classical-era Greek philosopher who put things down in writings had thoughts about natural science, mathematics, and the subjects that we recognize as distinctly "philosophical" today.

Readers of, say, Plato are often shocked by how his Timaeus, for instance, simultaneously provides an account of how perception works and develops the idea of a "Platonic solid," an achievement so important to geometry that we give it Plato's name.

There are complicated reasons for this. One is that Plato treats philosophy as the study of intelligible substances. For this reason, he of course thinks that mathematical objects belong to philosophy as much as studying other things. This might make it harder to understand why philosophy was also the study of the natural world, until you begin to see that Plato thinks that the natural world is a reflection of an intelligible substance.

But even when we put Plato's particular views of philosophy aside, the classical-era Greek philosophers inherit from the earliest philosophers that philosophy is "much learning." A sort of awkward phrase -- but the idea is that philosophers are people who know and want to know everything. Plato does engage with this view and tries to walk it back a bit in the Rival Lovers, but the thrust of it stays around for a while in ancient Greece.

That is why Aristotle wrote works like The History of Animals, Parts of Animals, as well as Metaphysics and On the Soul. Some of his (unfortunately) lost works include Concerning Mathematics, On the Unit, Concerning Optics, and On the Magnet.