I find it unbelievable that man developed stone tools 2.6 million years ago. With such tools, he would have dominated the earth. His population would have soared as there would be few predators against men armed with tools. He would have built structures and there would be far more record of his existence than we find.
I believe it is much more likely that the few traces of man we find at that age are actually far more recent and have simply been wrongly dated.
But the stone tools they are talking about that far back are mostly just rocks chiseled to have cutting edges.