In the world beyond the borders of the United States, there's a perception that American people aren't great with geography. They mostly know where things are inside their own country, but if you ask them to point to Italy or France on a map, the general belief is that the majority of them will struggle. That stereotype isn't helped much by the existence of t-shirts like this one.
Ironic t-shirts are a big thing, so it's possible that whoever designed the shirt made the error deliberately as a joke, but we don't have the context to confirm or deny it. What we can say without any hesitation is that this large continent is not Asia. It's Africa. It's bad enough to incorrectly identify a country, but when we're talking about a land mass of this size it's unforgivable!