Searching news archives doesn’t pull up any results for Palestinian American citizens killed in Gaza. I probably missed something if you’re so confident, so please send some sources if you have them on hand.
Designations of terrorism were more or less invented to deal with non-state actors. Which is why the definitions largely overlap with war crimes. If you’ll recall, the ICC are discussing whether or not to issue warrants for the arrest of Netanyahu, Gallant, Sinwar, Deif, and Haniyeh.