AFAIK, the (full) ISO includes only the basic stuff (at the time of creating the ISO) that it needs to be able to install Antergos, and also some tools that can be used for fixing potential problems, like gparted.
Note that the minimal ISO does not include e.g. gparted (although that would be a great addition to the minimal…).
The installer program on the ISO is cnchi. In the beginning of the install process, cnchi updates itself. This means you can use even an older ISO and it should be able to install Antergos like the latest ISO.
I have used an older ISO to install Antergos, but not many times so I don’t really know if it is possible to install Antergos with any older ISO.
Cnchi downloads most packages (including Gnome, KDE, etc.) while installing, so the new installed system is up to date.
So the ISO (AFAIK) does not include Gnome packages. Gnome is only the default choice offered by the ISO.