Brown sediments when frying meat
The brown color is given by the caramelization of the sugars contained in the meat. It is due to a chemical reaction that is triggered by the high temperature in the pan (take place between 140c and 180c or 284f and 356f) called Maillard reaction. It is exactly the same thing that gives bread and fried foods their characteristic golden-brown color and their delicious taste!

But back to the picture: the reason why you see the bottom of the pan becoming brown is because during cooking the meat lets some juices out. Those juices contain sugars that caramelize and stick to the pan or float in the hot grease.