To add to a sibling comment, the distinction is important, because observed mass of black holes falls largely into super massive (millions to billions solar masses) to stellar (dozens of solar masses). There is very, very, astonishingly few observed black holes with an intermediate mass. So, how super massive black holes form is a mystery, and finding large stellar mass black holes starts filling in (possibly) that evolutionary gap in black holes. Not a physicist, just read/watch a lot of pop astronomy/cosmology.

The distinction is clear and relevant because the mass distribution is strongly bimodal. A stellar black hole is the result of the gravitational collapse of a single star (well, or two at most). And maybe some of them have since then merged with a companion body. There are zillions of these in any given galaxy. Whereas there are maybe one or two supermassive black holes per galaxy, sitting in the center, with mass of millions or billions of suns, and we don’t quite know how they first formed and how they have accumulated so much mass. If the difference between "one" and "billion" doesn’t matter to you, well, ok then.

The difference is even more clear-cut because so-called intermediate mass black holes are something of a question mark. For a long time it wasn’t clear whether they even exist in any significant numbers, and even now the evidence is not especially rock-solid, especially with regard to candidate objects in the Milky Way.

Its not semantics. Its precise terminology. Ignoring this and redefining the precis terms because one lacks knowledge about the subject and arguing from faulty assumptions is a waste of everyone's time.

> I hadn't heard of the distinction stellar or non-stellar black hole before.

While it's possible that supermassive black holes were formed from stellar collapse, there are models where they didn't, while they _know_ that this one was formed from stellar collapse.