Spencer wasn't the only one who failed to survive the hour. Olivia, the friendly matriarch figure whom Negan already threatened twice (with death and sex both), took a bullet to the face after Rosita took aim and shot at Negan, missing him but leaving her homemade cartridge lodged squarely in the side of Negan's bat Lucille. Instead of retaliating, Negan punished Rosita for the act by determining who made the bullet in the first place. Negan appreciates the nerve of the thing: he actually seems to like Rosita, attempt on his life and all.
We know well that it was Eugene who manufactured the ammo on his own in an abandoned factory near the town, and after a bit more pressure -- Aaron's little-seen partner nearly lost his life too -- Negan discovers this little fact for himself. That's useful information and even more useful talent. So naturally, Eugene, once revealed for all his skills, got himself kidnapped and whisked away to the Sanctuary. Who knows what fate awaits the poor guy. Probably a bad one.