Where is "upstream" zlib 1.2.3.4 coming from?

[Török Edwin <edwintorok@gmail.com>]

Hi,

The Debian changelog for zlib 1:1.2.3.4.dfsg-1 says it is a new upstream
release:

zlib (1:1.2.3.4.dfsg-1) unstable; urgency=low

  * New upstream release.

However when I visit zlib.net (or zlib.org, or gzip.org/zlib they all
redirect to zlib.net), it has the same old zlib 1.2.3 from 2005. No new
releases.

So where does Debian get these new zlib releases from?

If I diff the ChangeLog of zlib 1.2.3, and Debian's 1.2.3.4 I see that
it has changes from 2006, and 2009, while zlib.net's
release stops at 2005.

The Debian package says "Homepage: http://zlib.net/";, which makes me
believe I was searching on the correct site for the upstream release.

Best regards,
--Edwin