It could be misinformation either way about the ability to detect it. If they were able to detect it, they may not want to let the Chinese know that they can detect. If they can't detect it , they may also not want the Chinese know that they can't detect it. They have known that these balloons have been going over the US for years (since they prob do the same with China and other countries). I suspect these balloons usually dip up and down from 100k or stay above 100k as that is consider out of territory/space. This instance could either be a "accident" where an error prevented the balloon to move back up or a purposely done event to troll on the US (Blinken).
If this disappears into the atmosphere and leaves the US it will be LOL from Team China
If this gets shot down and retrieved, it will be LOL for Team USA
If this "gets shot down" and never retrieved, both sides are giving face.
Former colonal says there is only a 12 mile window between the us coast and international waters that the US can legally shoot it down.