I don't get the saliva part. It's not like he was licking them and then replacing them back in the stock. If he picked them with his fingers and "popped them into his mouth" then his saliva would not have come in contact with the passengers' nuts.
I do think there is plenty to object to here. The FAs should not be eating the passengers' food before it's served. But this particular action doesn't make what was served any less hygenic. The FAs' hands are all over everything they serve. Plus the heating and the salt on the nuts would likely have taken care of anything he did pass onto the nuts.