It really, really doesn't matter. WhatsApp has the money to manipulate the law however they want. Small-time developers do not. I came up as an engineer in the bot development industry (for online games), and the history of the industry proves this. Historically, game companies like Blizzard[1][2] and Jagex[3] have managed to win multi-million dollar lawsuits against small bot developers, citing intellectual property laws; even though the defendants only ever created custom clients or injected code into clients with the permission of the players using them.

If gaming companies are able to use such absurd interpretations of IP law to win $7 million judgments against people who modify clients in-memory on end-user machines, then I'm sure a company with the capital of WhatsApp can destroy any open source developer that they want to.

[1]http://en.wikipedia.org/wiki/MDY_Industries,_LLC_v._Blizzard....

[2]http://legal.ceilingfansoftware.com/

[3]http://services.runescape.com/m=news/g=runescape/jagex-vs-ib...