The post looks at a Meatmeet BBQ Probe device and how it works. The device had two modes: one that runs directly through a mobile application and another that uses a cloud connection via passed WiFi credentials.
From using a BLE-Connect script they wrote in Python, they are able to see the UUIDs for each of the GATT characteristics. They grepped through the APK to get a list of files and luckily for them, the symbols were there for each one of the characteristics. So, they created a simple Python script to interact with the device for each one of the characteristics. Neat!
The article effectively claims that anybody can connect to the BLE device. In the various modes of BLE, there is no required pairing process; it's just simple to connect. The GATT services were likely usable without authentication at all. With other devices, even without keyboards, you typically have to "opt-in" to the process via a special set of button presses. It's weird that this wasn't the case.
Once you can connect to the device, it's effectively game over. The command remove_config could be used against the device to drop the configuration and add your own. The device even has over-the-air updates accessible as well. Naturally, there was no verification on the firmware either. So, it was a complete compromise of the device. They created a Botnet using this for fun. Good read!