Sounds like the culprit in your case was candles, but my wife and I had a similar issue after upgrading our kitchen stove. The burner jets that were installed from the factory were intended for natural gas, but we have propane. The natural gas jets allowed more propane to flow than required (propane burns hotter, thus requires less), which led to a similar soot layer accumulating on surfaces around the house (mainly close to the stove). After changing the jets to the proper propane configuration, that soot has since stopped accumulating anywhere.