Actually, traditionally Christmas day before the late 19th century was not a family holiday except for in some parts of the Netherlands - it was a day of drinking, caroling as an excuse for demanding free drink and food, partying and general debauchery. This went on to the point of such celebrations being banned in the 1600s throughout much of Europe (though they still went on).
Also, as expats who can't go home for Christmas every year, we throw a party for all expats to attend on Christmas night. It's always a roaring success. I totally agree that a party on Christmas Day in the USA or another Western country is probably not going to be well-attended, but that does not mean that all parties on Christmas day "go against tradition" (if anything they are a return to the roots of earlier Christmas practices) or that they are always inappropriate.
That said, the hostess was disgustingly rude when she called up the woman with children and screamed at her. So not cool.