Why would you ask if he came here illegally? Ghana does not share a border with the United States. Or do you think he swam all the way from Ghana to the United States?
Is this supposed to be a serious question? There are illegal aliens from countries all over the world in the US who have entered via Mexico and Canada. Or do you seriously believe that all aliens who enter the nation illegally are Mexican nationals?
Here's one story about Chinese illegals being smuggled in from Tijuana. They didn't swim over from China, either. Search the web and you will find thousands of incidents like this every year.
As it turns out, this soldier entered the US legally, and our nation owes him gratitude and honor for his service and courage. But that has zero to do with your map of Africa or the physical reality of the Atlantic Ocean.