Wouldn't a US citizen still have those obligations if they, for example, had committed crimes in Germany but just happened to fly back to the US before being arrested?
The US has no such treaty with Afghanistan, and is not a party to the ICC.
Whether or not the US should cooperate with the ICC is another matter, but the US has no legal or diplomatic obligation to do so. And in fact the US executive branch is required by US law to actively thwart ICC action against US servicemembers[1].
[0] https://en.wikipedia.org/wiki/List_of_United_States_extradit...
[1] https://en.wikipedia.org/wiki/United_States_and_the_Internat...