A compiler which compiles for a different arch is called a cross-compiler. Unless you explicitly asked for a cross compile, it is indeed surprising for a compiler to emit a binary that won't run on the same machine.
So she was originally compiling on a newer RPi, but immediately switched to compiling on the same one that couldn’t run it. And I believe the actual system images for RPi are built to support all models (there aren’t separate downloads for different models unless you want 64-bit) so it’s not crazy to think that everything would work building on a newer model.
This is just a packaging defect, Clang/LLVM isn’t being configured correctly by RPiOS (Raspbian).
This is what the post says:
>> This used to work in the old version (bullseye). It now breaks in the current one (bookworm). I figured, okay, maybe it's doing some optimization because it was built on the 4B. So, I went and did a build on the B+ natively. It also broke.
If that's not an explicit statement that she's compiling on the target platform, what is?