That's a drop in the bucket for a country that's already full of people from all over the world and constantly bragging about its diversity (despite looking very monocultural from the outside looking in).
At least legally, the US had no “rights” over Afghanistan. Afghanistan was not a colony, territory or state of the US. The government was “free” to kick out the US whenever they wanted.
In practice, US foreign policy doesn't recognize international law and never really has.
The US could annex Afghanistan, and apart from the CCP doing a lot of complaining about it (primarily because they want access to Afghanistan's mineral wealth), nothing would happen.