There is no stock iOS. There is only the Apple-provided iOS which you can't see the code and thus you can't actually check for anything. 

On WhatApp: "Depending on the request WhatsApp’s response may include, if available, basic subscriber information (such as their name, service start date, last seen date, IP address, device type, and email address), and account information (such as a user’s "about" information, profile photos, group information and contacts list). In the ordinary course of providing its service, WhatsApp does not store message logs once the messages are delivered or transaction logs of such delivered messages. In order to comply with a valid legal request, such as a valid Pen Register Trap and Trace Order in the United States, WhatsApp may start collecting message logs and call logs for a particular user indicating who the communication was to or from, the time it was transmitted and from which IP address, and the type of communication (such as a text or call)."

 https://faq.whatsapp.com/808280033839222