I’m not a lawyer, neither a license expert, so I cannot really comment on this. I’d love to hear more profound words from a license expert though 🙂
What I wrote in my blog post is how I understood Open Whisper Systems idea behind their usage of the GPL in their argument with Wire Swiss (you can read more about that here: https://de.scribd.com/document/311974670/Wire-Swiss-GmbH-v-Quiet-Riddle-Ventures-LLC )