I think the potential for art lies in the restrictions he could place on himself on receiving the items. At the moment he's just kind of enjoying the items and the process (wow, cool, a nice book.. some weird music heh heh..) , but if he perhaps made the item somehow central to his lifestyle - eg. he must tell everyone about what he receives / become an unquestioning advocate of whatever the robot chose for him to everyone around him - it would be more of a statement - how much do we let what we buy based on arbitrary values affect the way we present ourselves? or something like that...

It reminds me of an extreme Japanese TV show which used to be on, where a guy called Nasubi (after his long face - eggplant) - was locked naked in an apartment and could only live on what he gained from filling out thousands of "lucky draw" postcards. He gradually built up quite a system, gained bags of rice, a playstation..

人は懸賞だけで生きていけるか? - Can a person survive on sweepstakes?

The term "Generative" in "Generative art" has a pretty well-defined meaning.

Your comment is like saying that you don't think PHP arrays should be called "arrays" because element indices aren't necessarily strictly increasing. You can think that, and there's some sense to it, but it's still called "array". Similarly, you can't change the meaning of a commonly accepted term just because someone buys something at Amazon.

Assuming the OP's project can be called art, it's definitely generative. The artist does not choose which item is purchased.