Well, this sounds like it was before ANSI C, so there was no defined notion of undefined behaviour - I think that term of art came with the later standardisatio

Well, this sounds like it was before ANSI C, so there was no defined notion of undefined behaviour - I think that term of art came with the later standardisations. And if it was written to run on a specific OS or compiler (4BSD), one can argue that it was a really bad design, but it worked reliably on what was essentially the implementation-defined platform it was targeting.