Java Portable has been designed specifically for situations where Java support is needed but not necessarily guaranteed on the host system. The distribution is part of the Portable Apps collection and compatible with Java dependent applications that are offered on the site.
The portable Java installer can be downloaded from the Portable Apps website. It then needs to be executed to download the latest JRE to a location on the computer system.
The portable Java Runtime Environment provides the Java environment for applications of the apps suite.
Probably more interesting than this is the fact that portable apps offer a Java Portable Launcher which can be used to launch third party Java programs as well.
It can be that those third party apps are not necessarily portable in nature but that is the only difference there is. One benefit of this approach is that background processes like jqs.exe are not automatically running on the computer system.