So I just tried to replicate the query for the restaurant Da Nang Quan (which is in Oakland California) and this time it actually makes a sensible interpretation of my question ("Danang Quan") once out of five times, and got close another time ("Danang Kwan") and got complete nonsense the other three times. Unfortunately all three of the results it tried to give me for the nearly-right questions were in Vietnam which again is not anything like the answer I needed.

This confirms my experience so far with Siri.