I see this as being either a) a legitimate act of hate against black people, b) a prank or dare of the poorest taste, or c) a fake act meant to incite racial tensions (which we actually saw several of a few years back after the Jena incident). Any of these is really possible, even with the witness report. Until more information comes out, I guess we'll have to just wait and see.
I am curious though on what exactly this would be charged as. Is it malicious mischief or trespassing (although, I guess this would depend on whether they could be there or not)? I don't think it would be destruction of property since nothing was actually damaged. And hate crime laws only apply after a person has been found guilty (at least in Miss.).