That is just the problem, he wasn't treated as such. If he had been there would have simply been a military operation that he got killed in.
Instead 0bama made a thing about finding some heretofore never heard of loophole for an assassination and claims he had the authority as president to follow the recommendations of a secret panel.
They aren't the same thing and now there is a precedent for presidents to assassinate citizens on the word of unnamed operatives sans due process and sans legitimate military action.