After a (lost) match, in the XP/GP reward screen, I also got a "Spoils of War", a rare Datanode chance pack, obviously a random reward item. What's the mechanic there, how do I get more spoils?
In the before times, you'd always get a datanode after a match, but that has been changed long before this answer. Recently (August-ish), there was a short special event that rewarded players with a 'Spoils of War' pack after a match.
That being said, you no longer get datanodes or datanode packs for playing a match.
However, the datanode chance packs can still be purchased with Zen or GP from the marketplace.
Now it appears that any post-match rewards are called 'Spoils of War'. This includes things like GP tokens for completing daily missions.