How do you figure? They give the stuff to the public servants that have chosen careers that require them to be out on the street over their holidays as opposed to at home with their families as a show of support
Likewise, this place was giving a discount to people that chose to pray in public.
It's a fine line, but technically it is legal.
Now, am I saying it's moral or that I agree with it? No. I think it's a good way to cause a ruckus...
Discounts are legal. Discounts on the basis of a protected class, ie. race, color, religion, or national origin... are not.
http://www.law.cornell.edu/uscode/text/42/2000a