Typing people by what they wear almost never works. Its not reliable anyway. I have known a couple of triple positive types and esp core 7s dressing goth or dark. If someone dresses really weird what you can do is rule out the 369 tritype. But thats all. 4s are not the only type that sometimes dress 'weird'. Being unique is a universal need, so are all the Enneagram types needs. It's just over-exaggerated when its applied to a type, and deeply ingrained into the subconscious.
By the way, type 3s also need to be seen as unique way, but in a good "praise-worthy" way, whereas 4s subconsciously want to be seen as defective and unique in a negative way, like they want people to see them as the black sheep.