I major in computer science

All snarkiness aside... And I'm really not trying to be insulting here... You really don't sound like you know what you're talking about.

I mean - you can't make it far in a decent Computer Science degree program without at least a few lectures on how it's impossible to prove the absence of bugs. All you can do is test until you're unable to reproduce the bug any longer. That's why it's so important to have varied builds for testing. That's why the whole QA process is such a nightmare. That's why companies send alphas and betas out for the public to test.

So, yeah, a bug is a flaw in software that causes unintended behavior... But that's a misleadingly simple definition.

You seem to have interpreted "flaw" to mean that somebody actually typed something wrong, and that's just not true. In most cases the flaw is simply that they didn't think of some weird way their software would be used, or they failed to test on a certain piece of hardware.

And, yes, testing on varied hardware is important.

We call it "hardware" because we've gone to the trouble of burning it into silicon, but it's still code. And there can be bugs in your hardware just like there's bugs in your software.

Ultimately it doesn't much matter where you point the finger... Whether the "flaw" resides in your CPU's silicon, or the drivers that make it work, or the OS that talks to the drivers, or the game running on top of the OS... It's largely irrelevant. The end result is that your end-user is seeing unexpected behavior.

And that's why it's important to test on varied hardware. You discover that your game does something flaky on an Asus motherboard, or it runs like shit on an AMD CPU, or whatever. And then you can remedy that. You can figure out what it is that Asus or AMD or whoever is doing differently, and take it into account. You can modify your algorithms, or put in a separate execution path, or whatever.

Unless you're going to claim that Techland hates AMD and intended Dying Light to run poorly on that platform... Then you're going to have to accept that the poor performance is unintended, and therefor a "bug".

In this case I would suggest that the "flaw" isn't that somebody typed something wrong, but rather than insufficient testing was done on this platform.

But that's still a bug.

And regardless of whether AMD did something wrong in their silicon, or whether Techland did something wrong in their code, the issue is still being triggered by the hardware the game is run on.