The point is that they're inquiring to see whether or not he's Jewish. By the way, in some cases:
It is also an Ashkenazic Jewish ornamental name adopted in reference to God's promise to the Jewish people that they would be as many as the grains of sand upon the shore of the sea. Other spellings of the name include SANDGREN (sand branch), SANDMARK (sand territory), ZANDBERG (sand hill), SANDHAUS (sand house), SAND, SANDE, SANDSTEIN and ZANDSZTAJN (Polish). The Swedes have in recent times combined two words together to manufacture family names to take the place of their common patronymics, terminating in BERG (mountain), STROM (stream), ALM (elm), BLAD (leaf), HED (meadow), LUND (grove), SKOG (forest) and WAHL (field), to name but a few.