That it was not clarified afterward with "You mean x?" means that it was either an asset, Americans, or a highly specific group that was the sole subject of an investigation at the time. I doubt it was the random internet trolls they indicted, would have been mentioned if it was. So if they knew who they were, why weren't they indicted or reported in the Mueller report? No one would refer to a whole foreign non-allied nation or government, like Russia, as "our guys", so it cannot refer to "anything at all".