Them person who visited must know how close they got to others and that would be the main deciding factor before phoning and asking for testing - otherwise self isolate.
Fair comment, then if said visitor had close contact with the patient they should at least self isolate and warn others they have been in contact with.
Personally, I think they should. Even if they didn't come into contact with the carrier directly, chances are they came into contact with someone who did. Better safe that sorry.
Personally I'd not go out more than I needed to anyway, but if I wasn't showing symptoms then I'd not feel obliged to stay in. If the disease passes before there's symptoms there's litte chance of preventing it spreading anyway. Unless everyone stays isolated for a month or so.