Those articles are summaries explaining the findings, with much-longer detailed reports also available for download:
Both of these walk through the packet captures and provide a narrative around what is being seen in the discovery process.
A common finding between both reports is that the services are not using the more secure mechanism of DTLS for key exchange to set up encrypted voice channels. Instead they are using the older SDES mechanism that has a number of challenges, but, as noted by the report, is typically faster in enabling a call setup.
All in all the reports make for interesting reading. It's great to see both Facebook and WhatsApp using WebRTC and I think this will only continue to help with the overall growth of WebRTC as a platform. As an audio guy, I was pleased to see that Facebook Messenger is using the Opus codec, which is of course the preferred codec for WebRTC... but that doesn't necessarily mean that it has to be implemented by companies using WebRTC within their own closed products. Kudos to the Facebook team for supporting Opus!
Thanks to Philipp Hancke for writing these reports and I look forward to reading more in the series!