Before the 5.2 patch, a character with Relic Shield that killed a minion with Smite would trigger a spoils of war charge that would share the kill-gold with their lane partner. This didn't seem to be working last night, and I don't see a mention of this in the patch notes, so I assume it's a bug.
There is one possibility that would cause this and be intended (assuming they didn't change it). If you are bound to a Kalista, killing a minion she just hit will grant her the kill and not proc the FotM Spoils of War.
Other than that, I don't know, probably a bug.
Edit: Looking at your match history, there was no Kalista anyway.
I ran into a bot game to test this out, as I liked bringing smite on Blitz before they nerfed chilling. It worked. Definitely an isolated bug.
