Conspiracy theory:

US and China are in a relatively unknown (still relatively public especially with recent news) anti-satellite missile program race. The balloons you saw was practicing the return of modern observation balloons when satellites are taken out. Both nations have had space weapons since likely the early 2000s, with America having a lead in terms of “years” (likely had some in the 80s/90s) but eventually was worried enough about being surpassed that they are publicly mongering about it now.