It depends on the question you reply to. Accusative could be correct, too. "Is it a soup? Yes, goulash!" is without the suffix ("Ez leves? Igen, gulyás.") VS. "Would you like some soup? Yes, goulash" is with suffix ("Kérsz egy kis levest? Igen, gulyást!"). Once again note the different use of puctuation.
I disagree even more! Gulyás is a soup, even if some people use the word "goulash" for "pörkölt" instead, while paprikás is either a pörkölt modified with sour creme, or a sauce with paprika and sour creme, with something. Paprikás could be prepared with many kind of meats from chicken to wild boar or even mushrooms and it is always a "second plate" while gulyás is always a "first plate" soup with potatoes and beef or wild or even beans and pork. But never pork alone, and especially not chicken or turkey...
What would you say if I miss whiskey for gin? The difference is this big!