If you want to tackle something like this yourself, you might be able to use the bleson library. You can see an example of a script I wrote (based on another script) to sniff the BT temp and humidity readings from Govee 5072 sensors. All the BTLE messages received get processed so you could print them all out and look for the ones from the Chromecast remote (assuming it uses BTLE which makes sense that it would).
How did you wire this all? I see that thread. Did you sniff BT events (is BT that insecure?) and then posted on an MQTT queue for openHAB to consume? I am new at all of this… but I can learn 
. Especially with examples. Would MQTT be necessary, and simpler than, say, triggering something over the REST API? (At least as a first step.)