LP detectors will alarm on a wide variety of petroleum gases and some organic ones too - even dog farts are known to set them off. And contamination of th e sensor makes them extra sensitive.
As to why you have one with no propane anywhere, I suspect it may be just a glitch in RVIA requirements for that year. The RVIA standards have required an LP detector for many years, and it took a few years to get the standard to recognize that an all-electric RV is now practical. It may not have been an option to have no LP detector in your year (and the coach won't get RVIA certified if it doesn't conform to standards).
If you are sure there is no propane tank or device onbaord, you could just disconnect the power to the detector.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC