ZD, the rav may have held that you don’t have to be choshesh for treif’e utensils or remixing of the salad. (He excluded onions and radishes which are davar charif (sharp) because even a clean knife that wasn’t used in 24 hours would make it assur.) That part makes sense for your situation of sha’as had’chak/hefsed merubah. The part I don’t get is unchecked romaine lettuce; I assume he didn’t mean to include that.
Avram, I thinking telling the rabbi a whole megillah about a policy not to eat in others’ homes unless she knows them well would insult him. At this point, I think the less said, the better.