ORIGINAL: Dick T.
Your mind is safe. DA used to be a 3W dealer.
I surmise when they developed their own engine the franchise was either lost or surrendered due to conflict of interest.
DA did sell 3W engines long ago and that is a early 3W engine. That engine was called a 120, but it was really more like 112cc or so.
So yes, it is the real deal, but a very early version. You could always call DA and ask them about this engine.