It seems the only way it could not be a weapon is if the unintentional side effect was coming from some other kind of device (ex. surveillance) that is also spe

It seems the only way it could not be a weapon is if the unintentional side effect was coming from some other kind of device (ex. surveillance) that is also specifically targeted at U.S. diplomats. Surveillance of diplomatic missions does tend to use cutting edge technologies, so that's not entirely improbable, but if harming people wasn't the goal then it seems they would be concerned about it drawing attention to their technique.