In the U.S. at least that is just a fact of the statistics. The minority (black) population commits the majority of the crime. Whether you are prejudiced against black people (or any other race) because of those, or similar, statistics is up to you. I think that given the real world statistics for some places it is easy to see the irony in the picture/caption and find humor in it without being a racist, and without believing that all black people are criminals.
Again, whether you think the "opposite day" picture is funny or not is up to you. If you are offended by it then report it or talk to a mod. However, I think enough of them read this thread regularly that it would have been removed by now if they had deemed it to be racist and in breach of the AUP.