I also like to fact-check Particle. I did a few times during the Mesh launch and now I'm in a position to talk with Particle weekly on the Gen 3 Community Council. I cannot find where Particle touts "Thread Certification". All references I see, on their main Mesh Page, to Thread say "Build on Thread" like this:
Any assumption that they should be openly compatible with other Thread products is inferred. The link you posted to Certification | OpenThread says that the Nordic Semiconductor nRF52840 is a "Thread Certified Component"... it doesn't say anything about an end product using a nRF52840 chip. Furthermore, the certification for the OpenThread Border Router (OTBR) only applies to the Raspberry Pi 3B which uses an nRF52840. But you already wrestled with this concept in another post:
That's a selective quote on my part, but for a reason. The second half of the quote I take as a completely separate point:
I take the above as 2 separate, distinct points... one about gaining access to intellectual property (IP)... and the other about what certification means. While Particle may have accomplished gaining access to IP they do not seem to have sought or completed certification. Which makes sense from a business perspective. They were making a (private) ecosystem of IoT devices that communicate over a local network, not a Nest thermostat accessory. Thread provided a technology framework they didn't have to create from scratch.
If you do find Particle touting Thread Certification please let me know and I will gladly call them out on it in person.