Relevant parts:
Partner represents and warrants that it shall not introduce into WhatsApp’s Systems or Infrastructure, the Sublicensed Encryption Software, or otherwise make accessible to WhatsApp any viruses or any software licensed under the General Public Licence or any similar licence (e.g. GNU Affero General Public License (AGPL), GNU General Public License (GPL), GNU Lesser General Public License (LGPL)) containing a “copyleft” requirement during performance of the Services.
Partner shall not: (i) combine Sublicensed Encryption Software with any software licensed under any version of or derivative of the GNU General Public License (e.g.; GNU Affero General Public License (AGPL), GNU General Public License (GPL), GNU Lesser General Public License (LGPL) in any manner that could cause, or could be interpreted or asserted to cause, the Sublicensed Encryption Software or any modifications to the Sublicensed Encryption Software to become subject to the terms of any version of or derivative of the GNU General Public License or other copyleft open source software
GPL is a “copyleft” license aka a “viral” license. It forces anybody who uses it to keep the software open but not just the code, also the way it is being used, and to use the same license if they modify the code, or distribute anything made with the code, and these terms are perpetual and unrevokable.
Basically anything GPL will keep being GPL and anything that comes into contact with it will have to be GPL or take certain precautions to avoid becoming GPL.
Thanks for clarifying. I have read something like this but now its more clear.