This quote does not exist on the page, but it is understood within the page that if a non-Jew loses an object, a Jew is not required to return it. 

One of the 613 commandments in the Torah is to return a lost object to its owner (Deuteronomy 22:1).  There are numerous details involved with this commandment, including whether or not the item has some identifying mark, how difficult and expensive it will be to return it to the owner (you’re not required to spend hundreds of dollars to return an item worth a buck), whether the owner would likely have given up on recovering the object and much more. 

Like most of the commandments in the Torah, this only applies to Jews and for Jews.  As a result, it is true that a Jew is not required to return an object lost by a non-Jew.  By the same token, it’s equally true that a non-Jew is not required to return an object lost by a Jew, since non-Jews are not bound by the commandment to return a lost object.

In any event, there is certainly nothing that says that one cannot go beyond the letter of the law and return it anyway.  For example, the Chofetz Chaim (Rabbi Yisroel Mayer Kagan 1838-1933) was known to return even small amounts lost by non-Jews.  Many Jews today also act accordingly.