You should always listen to context. Languages are not competely logical.
The United States of America (USA or U.S.A.), commonly known as the United States (US or U.S.) or America, is a country primarily located in North America, between Canada and Mexico.
This has been pretty much true for every country I have visited or lived in, except one time in France some one referred to my Canadian cousin as American.
“America” or “Americas” can refer to the continents which is why you should pay attention to context. When someone says they have an American citizenship, they are not citizens of a continent.
In this comic, if someone is in North America, when they say America, they are referring to USA.