Acid-catalyzed hydrolysis of diphenyl malonate
If the question is "What are the products of hydrolysis of diphenyl malonate?", then my answer would be 2 equivalents of phenol and one equivalent of malonic acid.

If the question is "What are the products of diphenyl malonate when heated in an acid aqueous solution?", then my answer would be 2 equivalents of phenol, one equivalent of acetic acid, and one equivalent of carbon dioxide.

I see it sort of as a semantic question, since the hydrolysis of an ester gives an alcohol and a carboxylic acid, as you suggest. I don't consider decarboxylation to be a hydrolysis reaction, literally defined as cleavage of bonds by addition of water. Water isn't incorporated into the products of the decarboxylation step.