I think the answers by Peter and Mohit Wadhwa might reflect what I see. I don't think either sentence in the question is wrong. To me, the difference is more of a nuance that makes the second a better fit.
People would understand or figure out the intent of the first sentence from the context. But it sounds a little off to my native ear because it is unnecessarily ambiguous and it would be more natural to just use more precise wording; words more typically associated with the situation.
"Clothing" is a collection of individual items and isn't usually the word of choice if you are talking about a coordinated outfit.
"Appropriate" has many possible contexts, even in association with a job interview, especially if you are referring to a collection of items rather than an outfit. For example, dressing in consideration of the weather, the amount of coverage in terms of modesty, clothing and shoes that facilitate activity if the interview might involve extensive walking or other exertion, etc.
An appropriate "outfit" or "attire", on the other hand, goes to the appearance and coordination of the items; how they look together. Either of those terms wouldn't preclude consideration of the weather, modesty, movement, or other characteristics, but the focus would be on "looking the part" or "dressing for success", which would be the intended meaning.