The Economist originates and has primary readership, in the USA. In that country, the term "America" is used to refer to "United States of America." When referring to the American continents, the common terms are "Americas" (note the plural form) or the explicit forms North, Central, and South America. Most people in the United States are aware that the United States does not span the entirety of any or all of the American continents. As a simple example, most Americans are aware of the country north of the USA border called Canada, which is also in North America.

Hope that helps.