That happens, in this universe. You get something hot, say a cup of coffee in the microwave, or your neutralization reaction. After a while, the object loses it's heat, to the environment, and gets cold. A giant pot of water stays hot long after you stop heating it. A cup of coffee get cold sooner. Your graduated cylinder even faster. Heat is heat. There is nothing special about the cooling properties of a solution of hydrogen chloride gas in water (HCl,) or NaCl, as is the case when your reaction is complete.