While you aren't wrong that every automated system needs human oversight and occasional intervention, when the average person hears "fully automated" or any of the many marketing terms used for these things lately they are going to take it pretty close to face value.
It also doesn't help that it was largely marketed and reported on as if it wasn't an experiment, but a solved and working "product".
Every system will have its own requirements and acceptable margins for error and required interventions, but I think most people would feel that even the one in twenty (5%) goal is a lot for a project like the Amazon automated shops. It would be a lot for any of the automations I come into contact with (and have built) at my job, but admittedly I'm not doing anything as remotely novel or as complicated as an unattended shop.
Beyond that, people have a lot more reasons to dislike these systems than just the amount of human intervention and I think they're just going to jump on whichever one is currently being discussed in order to express it. Like displeasure that the teleoperation positions are outsourced the way they are, taking even more jobs away from the local population.