The upside-down thing is not exclusive to the USA flag. Regarding the Australian flag:
To fly a flag upside down is a signal of distress. The Australian National Flag should not, therefore, be displayed with the Union Jack down on any occasion except as a signal of distress.
So it's kinda displaying an "SOS" when you don't actually need assistance, I guess?
But as with all symbology, it gets constantly resemantified by the circumstances. Given this article it seems that it's starting to become a bit of a cooker thing: https://www.abc.net.au/news/2026-05-11/upside-down-flags-protest-regional-victorians/106592092