How can one be sure that group of bone fragments belonged to a member of our species? Note how tiny and incomplete that section is.
The same way a good CSI can tell a human bone from animals at a crime scene. Certain bones and bone structures have only been found in humans, there direct ancestors and some off shoots. Certain other bones and bone structures are only found in modern Homo sapiens, now these can and have been misidentified, but the scientists involved try very hard to prove what they say before they report it because nobody in the scientific world wants to be found a fool. If these are not in fact what this scientist claims them to be and some other scientist proves it then the original scientist would lose funding and respectability along with all his other published works coming under more intense scrutiny.