Reciting the Pledge of Allegiance is not a chant."Chant" is an appropriate word for a group of people all standing up and reciting the same thing in unison.
Even if it is the Pledge of Allegiance, it is inappropriate in this context. The group should have arranged for a private dining room for their event, or they could have rented out the entire restaurant for the evening if they really wanted to have their event there.
But, what they did was inconsiderate and disruptive to the rest of the restaurant's customers.
Olive Garden never complained about them saying the Pledge.
Your bringing it up in this context is just a "red Herring."
I use the dictionary to determine whether a word is appropriate in the context of an article and there is no way these people were chanting anything.