The code quality apparently was abysmal and full of dirty hacks due to a mix of "beginner energy" and "go fast & break things" Silicom Valley mindset. The issues with bun (leading to the big Anthropic hack) were subtly blamed on the Zig language, even though Zig is completely fine; Bun's code (which already was full of bad generated slop at that point, as well as code by programmers who were treated badly -> more bad code) was just crap.

After Zig was blamed the Zig creator wrote a blogpost detailing all of it. Worth a read, certainly more human than the corposlop Anthropic announces.