YES! This "Chris' tuna salad" is my personal nails on chalkboard moment. (And you are correct....in most stylebooks, it is only with classical names that the "s" name ending does not require apostrophe plus "s".)It annoys me when people misspell common words, especially when it is obvious they know how to spell them and were just careless.
Also, I'm of the opinion that a possessive isn't different if the word ends in "s". It is Chris's tuna salad.