to clarify: Open source software is generally published under a version of the GPL (GNU Public License, more info at: The GNU General Public License v3.0 - GNU Project - Free Software Foundation (FSF)
While Linux and Android are Open source (this means that the source code is available for anyone woth the relevant shills to ownload and modify, provided all such modifications remain open source, and upstream contributors are credited for their work.
Most Apps however, are definitely not open source and copyright remains with the creators. Just because Linux, Android or any other OS is FOSS (Free, open source software) does not mean that all Apps running on it are. While it is legal (and encouraged) to redistribute Open source software, it is most definitely not legal to redistribute copyrighted Apps/music/boks etc.