I totally remembered that you're Jewish and here's the Hannukah card to prove it! -- Notice that this is presumably from a non-Jew to a Jewish friend. This strikes me as a "very American" card. Traditionally, Jews considered Hannukah to be a rather unimportant holiday on the religious calendar, but in 20th-century America, Hannukah gradually evolved into a sort of "Jewish Christmas", at least in the popular imagination.

And in some ways, the elevation of Hannukah was not so much about showing respect for the customs of Jewish Americans, but was related to the perpetual arguments in US domestic politics about religion in public schools, and representation of minorities, and church/state separation, etc. Thus, there are tens of millions of Christian Americans who are mostly ignorant of much more important Jewish religious days such as Yom Kippur, Rosh Hashana, Purim, Sukkot, etc. -- but they remember Hannukah, because it comes in December, near Christmas!

Thus, there's quite a lot of ironic humor in this card -- presumably, the sender never sends Rebecca a card on more important Jewish holidays like Rosh Hashana or Purim -- but when Christmastime comes around, the sender suddenly recalls, "Oh yeah, Rebecca is Jewish -- I should send her a Hannukah card..."