| Completely Random. From what I gather though, loot is generated when a monster is spawned. So the moment you zone in and the instance is created, loot is determined. They've said over and over that the RNG they use is not a seeded generator. Raid group voodoo will not change loot.
That said, theoretically, if an ID generates the instance, then it's possible that the mobs are all spawned in the same way, and that would explain the same boss drops when the Raid IDs were not reseting properly. This would not be a case of "raid seeding" but a case where the instance spawn determined the ID.
Human beings always like to see patterns in static. Any preceived streak is not a result of RNG's not being random, but of human cognitive function looking for a pattern. | 