Very curious what exactly this is.
Blowing up the grainy first photo and comparing it to the Matrixbrute, you can see the part toward the right that might be a mtrix is considerably smaller. On the Matrixbrute its over an octave wide, almost an octave and a third. The unidentified keyboard it is only about a fifth wide, and looks square. The Matrixbrute is slighly wider than it is high.
Good sort of mystery.