This was not slotfilling, @Alex. The alliance war distinction that Sphinx made refers to a time when you should expect as an alliance leader for your members to be triple slotted and so yes, sending people to hit them is intentionally blocking that. That's not an assumption you could generally make in peace and, in this particular situation, E404, a non-pirate alliance in a sphere, generally wouldn't be triple slotting TCW members unless declaring an alliance war because that is an act of war. If they were declaring an alliance war, that would be exceptionally easy to spot as there'd be a multitude of wars between those two alliances. To say that alliances will permawar each other to keep each other from getting hit will never happen because the only way to effectively do that without achieving the same outcome as being warred is to not fight at all and just hold the slots. Ergo, actual slotfilling.
This was an alliance raiding its own members to recover cash from a member they hoped would wake up but isn't guaranteed to. This is a practice several alliances do and have done for years, a practice which you have ruled previously to not be slotfilling. Most members don't switch policies because they aren't raiding consistently and no one ever remembers to change policies in peacetime. They attack with smaller units than they would during an alliance war or even than a career raider would sometimes because it's a one-off raid, it's supposed to be economic. Your goal is to beige, the loot along the way isn't the primary objective and most alliance have minimal military on them during peace as well. They aren't going to max out their military for a single raid - that's expensive and ill advised.