Surveys suggest that the proportion of American households that own guns has declined from about 50% in the early 1980s to about 35% now. (These figures are subject to sampling error: when men answer the phone they are more likely than women to say there is a gun in the house. But repeated surveys tell a consistent story.)
That statement is clearly not reflected in the Gallup Poll. The author should written that a survey (The General Social Survey) shows this. The Gallup survey, which asks about guns in the household, shows a different pattern. Below I modify the figure on the Gallup site to include households where guns are on the property (such as the garage) but not necessarily in the house itself. This does not show a downward trend at all: the average over the 1980’s is 44% and the average since 2000 is 42.5%. Since 2000 Gallup has also asked whether or not the respondent is the owner. The percent of gun owners hovers around 29% over that period with no clear trend.