I dunno, why did they? I think if you are concerned about it and I'm not, you are probably the one that needs to explain.

Maybe they are planning to drop an insignificant number of small munitions on random locations in the US or something.

I haven't yet seen a compelling reason to think it is either Chinese or an espionage craft anyway,other than news reporting "the Pentagon sure thinks so"

Update since i posted: chinese foreign ministry has confirmed, says it's for scientific purposes