rsync has a ton of HFS+ specific code. Making a faithful duplicate of a file (specifically its metadata) is a feat on its own: http://blog.plasticsfuture.org/2006/03/05/the-state-of-backu...
Even here, there isn't special casing for HFS. Instead, a special library function, copyfile()[1], is used to handle copying files and their associated metadata.
It seems this function was introduced in Mac OS X 10.5, which was after the article you linked. I'd wager copyfile() was introduced in response to the unwieldy file copy mechanics.
After discovering how copyfile() is used in rsync, I am fairly confident that rsync works so well on the new FS as a result of Apple implementing a fairly solid copyfile() for APFS.
[0] https://opensource.apple.com/source/rsync/rsync-20/patches/E... [1] http://www.manpagez.com/man/3/copyfile/
https://github.com/Homebrew/homebrew-core/blob/master/Formul...