"When you have eliminated all the possible whatever remains (no matter how improbable) must be speculative assumption" (Barret Homes, 1878)
Caudrons seemed to have a wide variety of engines - possibly adapting batches to suit whatever engines were available. My wife's great uncle was an RFC pilot - hanging in my study I have a propeller blade with several pictures set into it. One is clearly a Caudron, but this one seems to have a non-rotary engine:
Other pictures on the prop include a vickers gunbus and a Sopwith 1-1/2 strutter.
PDR