What suggests the family in Vladimir Nabokov's "Signs and Symbols" is Jewish?

Although Nabokov does not explicitly state the couple in this short story is Jewish, he does hint to their Jewish ancestry. He suggests several times in the story that the couple is not originally from New York. The husband is described as being from “the old country.” It is also mentioned that they left Europe when the boy was ten. At one time, the couple lived in Minsk, an area heavily populated with people of Jewish descent. Furthermore, when looking back at her pictures, the mother mentions two Jewish surnames, Borisovna and Soloveichiks. Aunt Rosa is also mentioned as a person “put to death by the Germans,” suggesting she was a Jew during the Holocaust.
The story is set on a Friday evening. In Judaism, Sabbath begins on Friday evenings and Jews celebrate with a Shabbat dinner. The mother stops at the store to get fish for their supper, a traditional Shabbat meal. 
Vladimir Nabokov gives several details in the story to suggest the family may be of Jewish descent.