It’s not only that the Chinese restaurants are conveniently open on Christmas. Lacking in religious imagery (unlike, say, Italian restrurants), they were more welcoming to Jews. The Chinese and Jewish immigrant communities on the Lower East Side of New York and in other urban landing zones were in close proximity, and by and large the Chinese did not discriminate against the generally persecuted Jews. In return, Jews embraced the Chinese establishments, which were local, inexpensive, and seen as exotic and urbane.
Furthermore, there was not much dairy in Chinese cuisine, so little risk of violating the kosher prohibition against mixing meat and milk. And nonkosher ingredients such as pork and shellfish were generally finely chopped, embedded in sauces, and/or mixed with rice. Thus their non-kosher nature could more easily be ignored. For some East European Jews, Chinese food, although exotic, included attractively familiar elements such as sweet and sour flavors, egg dishes, and pancakes reminiscent of blintzes.
via Mental Floss