Source code being visible doesn't make it open source. It had a personal-use-only license, which isn't a valid OSSI license (which is what makes something open source).
That's why I qualified it with "if that's what you mean by closed source". I don't know if all source is either open or closed and anything that isn't OSI-approved is closed. I don't think that's what people usually mean by "closed source".
I also freely granted that dmd's ad-hoc license wasn't open source despite having visible source.
I also freely granted that dmd's ad-hoc license wasn't open source despite having visible source.