Saturday night (October 3, 2020) a group of people assembled outside Walter Reed Hospital. They seemed to waving Trump Campaign flags and the national flag of East Turkestan. Why?
If you're referring to this (light blue flag on the left):
Then yes, that is the East Turkistan flag, and is likely being flown by people trying to draw attention to the oppression of Uighurs by the Chinese government. It isn't uncommon to see people sneak side-demonstrations in at places they know public figures and the media will be, and the East Turkistan flag is obscure enough (to American eyes) that it might be mistaken for some off-beat pro-Trump messaging.
Though it is a bit surprising no one did a double-take at the obviously Islamic symbology...
I saw this flag in two images of the supportive demonstration; in one it was incongruously at the very center of the mass of flags. But I'd be curious to know how long they were able to stay there until someone worked through the 'which of these things is not like the others' game and asked them to leave. No one in the news media (that I could find) seems to have caught onto it, so no one has followed up.
EDIT: Per comments, the East Turkistan National Awakening Movement has taken credit for the flags, wishing Trump a speedy recovery and asking him to take stronger action against China for their treatment of the Uighurs.