This is a TextMate/Sublime/VS Code/Atom bundle providing language support for x86_64 assembly language in a variety of dialects (nasm/yasm primarily, but could highlight tasm/gas to some extent).
Atom package is exported from Textmate/Sublime Bundle, all issues and pull requests should be filed there.
To compile the yaml sources to tmLanguage, you'll need PackageDev.
Good catch. Let us know what about this package looks wrong to you, and we'll investigate right away.