I wasn't suggesting she should "scoff" at the bite, but even minor skin cuts/scrapes often develop an easily-treated, minor localized infection. Our skin is covered with potentially pathogenic bacteria, especially Staph(ylococcus), so that's not too surprising. Usually it's not something to be particularly concerned about beyond taking routine home fiirst-aid precautions.
As for that article, keep in mind that it also notes that only ~20% of all projected dog bites are reported in the first place. Presumably it's the more serious bites and ones actually showing signs of infection that do get reported, so the likelihood of any given dog bite becoming infected is probably much lower than 1 in 5. (If I'm not misremembering my negligible knowledge of statistics, only 3-4% according to the article's numbers. Edit: That estimate is too low. NVM)
And as for tetanus, specifically, it isn't even mentioned in that article. There are, in fact, many fewer than 100 reported cases of tetanus per year in the US from all sources, and since it's caused by anaerobic bacteria, pretty unlikely to be present in an animal's mouth.