It might be advisable to take their point in good faith by considering what they may be saying instead of resorting to mentioning something about US foreign policy.
Based on the definitions I can find of murder in various dictionaries, it seems almost universally defined as an unlawful act. If you choose to go by the commonly-accepted usage of the term, it would not be a murder if the killing is found to be lawful. There are other words, such as homicide, that could be used here [1, 2]. The CPS themselves (in the UK) have a whole page about this distinction.
I was just pointing out that definitions can be really flexible. Sure, murder is a crime of intentionally killing someone. So if something is not a crime then it's not a murder. But since criminal law is vast and varied same deed in one country might be a crime and in other it is not. I used the word "murder" in non-US definition of what crime is. And pointed out that such actions are not a murder specifically in USA. Implying that with respect to other countries laws they might be. And they are.
And calling indiscriminately killing people "a foreign policy" and legal is another can of USA made worms.
Check out how narratives created and pushed by evil people affected your moral sense.
And by definition anyone in drone weapon blast radius is enemy combatant.
In USA.