Engineers use software and inevitably some will improve the software as they use it. I’d draw a distinction between engineering using software, and engineering the software itself, though. It becomes a bit blurry—I’d say using the Matlab command line is not necessarily software engineering, it’s using a tool for engineering that happens to be made of software. But you can also write your own Matlab code, so if we want to say there’s software engineering I guess there’s no reason it couldn’t be done in that environment.

IMO, I’ve never been all that concerned as to whether the “engineer” label should apply to me (coming from an engineering education but mostly looking at software). It’s more about having a professional obligation than any great feats of skill anyway, and since an obligation is mostly just felt in your head, you can give it to yourself.