"Waterfowl that ingest 1 or 2 shot more often live than die, and waterfowl tend to pick up only a small number of pellets at any one time: 65 percent take one shot, 15 percent two shot, 7 percent three shot, 3 percent four shot, 2 percent five shot, 1 percent six shot, and 7 percent seven or more shot (Bellrose 1959:260). A compilation of reports on the incidence of shot ingestion by mallards during the 1970s and early 1980s provided findings similar to those of Bellrose. Of 1,211 mallard (Anas platyrhynchos) gizzards containing shot pellets, 63.0 percent contained one pellet, and 13.6 percent contained 2 pellets (Table 2)."
I copied the above from an article published on a USGS site, Northern Prairie Wildlife Research Center.
A link to the report.
http://www.npwrc.usgs.gov/resource/birds/pbpoison/ingested.htmBased on the article, the possiblity exists that waterfowl can die from 1 pellet ingested, but the chance is greater that it will live.
Based on your last paragraph, it sounds as though the ID F&G survey taker was emphatic in his statement that a duck or goose will die if just one pellet is ingested.
I'm waiting with for the ID F&G call!