Was UNIX open source?

No, but XNU (Apple's OS kenel) is based BSD which is open source. In fact XNU itself is open source even though its BSD licenced so does not have to be. https://github.com/apple-oss-distributions/xnu

There even seems to be an open source variant of the OS https://www.puredarwin.org/

And that has to do with the price of tea in China how?

You asked whether Unix was open source in the context of a macbook. The Unix derivative used on a Macbook is, indeed, open source.

No, I asked if Unix was open source. The macOS kernel is a BSD derivative. BSD != Unix. If the comment was to hold true, they should have said BSD wants your MacBook.

> The macOS kernel is a BSD derivative. BSD != Unix.

BSD is derived from Unix source, so it is Unix. Most BSDs cannot be distributed using the Unix name because of lack of trademark permission. However, MacOS is an officially certified Unix: https://www.opengroup.org/openbrand/register/