Throughout the rest of the course, America is accepted for Marekani, so I think it's just an omission here. It should be "
the USA" or "
the US" though.
Also, in English, "America" virtually never refers to the Americas as a whole - a fact which seems to annoy a lot of Spanish speakers because that is the meaning of their word América. When we refer to both continents together, it's "
s" or individually "North America" and "South America" (as well as "Central America" as a part of North America).