And rightly so, because that statement would make no sense.
Saying that humans are more unique than other species, however, and including cooking food as one of the unique features of the species that contributed to that assessment, could be fair game (though that would be a ludicrously complicated assessment that could never hope to be comprehensive enough to draw any definite conclusions and I'd dismiss it on those grounds).
In that case, none of the vases are unique because they're all vases. Or if one was more of a jar instead of a vase, none of them are unique because they're all made of clay. Or if one of them was made of glass instead of clay, none of them are unique because they're all silica-based. Or if one of them was made of metal instead of some manner of silicate, none of them are unique because they're all man-made. Or if one of them was a naturally-occurring rock formation that just happened to be the right shape to be used as a jar, none of them are unique because they can all be used to hold things.
Nothing is truly unique. If you dig hard enough and interpret "kind" loosely enough, you can find commonalities between any two objects that mean they are not "one of a kind." That means that, for the word "unique" to have any application at all, it has to be framed as "unique, except for all these other aspects in which it isn't." That qualifier is not binary, and given that that qualifier is the logical complement of the usage of the term "unique," that means the usage of the term "unique" must also not be binary.
Is it not? Why would somebody who achieves uniqueness more frequently not be considered better at uniquing?
They say it to communicate the point of "this thing more noticeably stands out as being unique," which in turn means the traits that they have assessed have qualified as "unique" within their colloquial scope with remarkable frequency. It's not wrong to say that "more unusual" is perhaps technically the better way to phrase it, but to use "more unique" to mean "I've identified your traits as being unique more often than for those to whom I'm comparing you" is well within the bounds of reasonable colloquial logic and easily understood by everyone involved.
This is complete and utter idiocy. To be the only one of its kind does not mean that it needs to be unique in every way. If one thing sets it apart from all others, it is unique. Its such a simple concept.
Like, if theres a single purple dog in the world, that dog is unique. You wouldnt say he isnt because hes got four legs just like all the other dogs. How can you not understand that?