Well, I am not that familiar with it, but given how much attention they gave to optimizing this, my best guess would be that they made sure that similar product

Well, I am not that familiar with it, but given how much attention they gave to optimizing this, my best guess would be that they made sure that similar products didn't get similar codes. And I guess for a grocery store, mistakes aren't that big a problem, especially for ones that mostly don't sell anything but their own brands (and thus normally don't have all that many similar products at different prices anyway). Also, yes, the rumor always was that Aldi paid well. Presumably the savings in additional staff and space and cash registers was still worth it.