I suppose one difference is that the pieces from Perserverance were _supposed_ to land on Mars. Whereas this object ended up floating around uselessly, like so much other "space junk". And because they suspect it's origin as being China, it makes sense to write it that way. Chinese junk, American junk, Canadian junk, although even these could be softened by "Chinese space junk, American space junk"... I wonder though if it is also being used in a retro sci-fi manner, in that there are crafts called "junks", particularly in English, "Chinese junks". See https://en.wikipedia.org/wiki/Junk_(ship) and https://www.newworldencyclopedia.org/entry/Junk_(ship)#:~:te.... Thus it is a chance to use the term for a sailing craft in a new context - a Chinese junk, but in space!