I also do this sort of thing all the time. From your description you were not playing to the dining room, you were playing to the bar and typically management wants you to keep it down so you're not too loud in the dining room. Unless you were actually hired by the corporation for their party, you have no expectation of anything from them. In fact, they may have been upset because you were interfering with their function.
The regular Friday evening 7-10pm gig I have at a place that appears to be the same set up ie two rooms split by a partial glass divider, does not use any bands during the holidays because of all the private parties. If any of those want entertainment they will hire it themselves but the restaurant doesn't start the music in the bar until 10pm and unfortunately it's the usual loud thumping disco.

Bob

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