"Worse is better" is much older then "undefined behaviour". Undefined behaviour was invented for C standardization, when C was already mature and had been out of the Unix childhood home for a long time.
For example, many UB semantics in the standard come from allowing for C ports for strange non-unix hardware, and making bold decisions when developments in compiler optimization state of the art ran into underspecified corners of C semantics.
"Worse Is Better", as a description of a set of engineering values embodied by C, is from 1989.
I'm taking your word for it that UB was invented for C standardization (I have no knowledge of that history, and your claim seems plausible), and I'm going to say that probably they didn't invent it in the last year of the seven-year standardization effort, so probably UB is older than Worse Is Better.
For example, many UB semantics in the standard come from allowing for C ports for strange non-unix hardware, and making bold decisions when developments in compiler optimization state of the art ran into underspecified corners of C semantics.