The implied supposition is that we did not know the balloon was air born until it was over the US or at least over North America; it is unclear which from the article.
For that to be true, it would mean that we do not monitor Chinese air traffic from space.
That is false
There is much the ChiComs would like to find out, the extent of our capability being a primary goal.
Hence this, "garsh, ya took us by supprize" public stance.
Even shooting it down as it approached our continent would have let them know a lot.
Should we have said, "yeah we been laughin at your derregible since the ground crew rolled it out of the hanger"?
No, we should do exactly what we did.
That's why the military would not shoot it down days ago when Biden wanted to make political hay. His crap in this case is no worse than the republicans trying to use this against him.