This is not a case of a broad generalization based on few instances, because the author is referencing data about the country as a whole. GDP is a sum of the entire nation's spending and earnings. This data is actually quite extensive. A generalization based on a small sample would be more like this: "The people of the United States are not lightly taxed, because my neighbor Bill is always complaining about his high taxes."
The real problem is the last statement: "This 7 percent, then, amounts to tax." Just because healthcare is a tax-based public expense in other countries, that does not mean that healthcare costs should be considered a tax in the United States. The author spent the whole passage explaining that Americans pay for healthcare out of pocket. It seems like the author believes that healthcare should be paid for by tax revenue, but it isn't. The author extends the word "tax" to mean expenses that he/she believes should be a tax. This is why B is correct.
