> This is not a C compiler.

This is technically true! What is posted here is not a C compiler. It is an implementation of a subset of C.

I'd prefer that the title honestly mentions that like: A compiler for a subset of C that fits in the 512 byte boot sector.

It is still a remarkable feat. But honestly, when I read the original title I was in complete disbelief that someone could implement a whole C compiler in 512 bytes.

But with the new context that it is a subset of C (not the whole C), the initial great surprise is gone. It is still very impressive though.