That likely has to do with MLB being on many platforms. Sony wants more developers that can work on many architectures to move them around.... Knowing they can do that also means when The Last Of Us 2 is done, they can move them to work on MLB. Also, many programs in games still use NVIDIA, understand that PS4 or PS5 using AMD, doesn't actually mean none of the programs at their offices run on NVIDIA. So it sounds like they want any programming experience as the more they know, the more they can do.
So the issue is simply that most gamers don't actually develop games, thus have zero clue what it takes to make one, thus think using a PC means the title would be on PC, if you look back, Sony, Nintendo, MS, Rockstar and many others ask for this and still don't put out PC titles on those projects even with them asking for that experience. It simply means they need someone that CAN DO THAT, not that all projects regarding that will be on PC. Look at many job postings and you'll see that.
For example.
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So when is Nintendo putting their games on PC? MUST be happening right?
"Development experience on Unix, Linux or Windows " yup, confirmed, Mario Kart, Zelda and Smash to PC /s