On what basis would this decision be rendered? The funding was lawfully appropriated by an act of Congress, and the Georgia state government contracted with Senior Citizens Inc. to dispense of these funds. Unless the contract explicitly prohibits overt displays of religiosity during the purveyance of these meals, there would be no legal standing for imposing such a prohibition.I don't think it caries the burden of it, but if such things are decided, those who eat the free lunch can always choose to not accept the free lunch and continue to practice overt religious displays.
It's only unconstitutional if they are forced to not pray in any and all circumstances.
But in this case they can gather prior to the meal at a separate location and pray as a group if they wish, or they can find some other way to get a free meal that doesn't have said restrictions and pray as group before they eat.