How would you define "quality" in this context?
One could also say that quality is related to the functional output.
Right, I said nothing that contradicts that ("High quality code isn't just code that performs well when executed, but also ..."). High quality functional output is a necessary requirement, but it isn't sufficient to determine if code is high quality.
My point was that it's all subjective in the end.
Imagine writing a very good program, running it through an obfuscator, and throwing away the original code. Is the obfuscated code "high quality code" now, because the output of the compilation still works as before?
Do you mean how well it was written, or do you mean how well it performs? Or do both matter? Equally, or one more/less than the other?
It probably depends on whether you're the developer taking over the codebase, or the customer running the code in production..
Take video games.. A lot of it is messy spaghetti C++ code, not modular or well structured, full of hacks and manual optimizations, to give the best possible performance on available hardware.
It might be impossible to parse or maintain, but it does the job about as well as possible, which is really all that matters to the end user. I would call that high quality code.
So again, subjective...