Although I think he might have been pointing out the problem of reproducible builds[2].
[1] https://github.com/dotnet/roslyn/issues/372
[2] https://wiki.debian.org/ReproducibleBuilds/About
[1]: https://nixos.org
[2]: http://www.gnu.org/software/guix
[1]: http://wiki.baserock.org/
[1]: https://nixos.org
[2]: http://www.gnu.org/software/guix