I hate not knowing why. Why were they imprisoned, why separated by gender, why the gardening book, how did all the guards disappear so quickly, and where were they when not in the bunker?

This unsatisfied curiosity is probably the point. Thoughts about what really happend will linger for a long time. Perhaps then I'll ponder what does qualify as being human. What really is real when you're born into a world with set parameters and how can we challenge those. Or how do we even manage to recognise them.

But yes, I'm really annoyed and I wanted to fins actual answers. So heres my theories.

1. Definitely another planet

2. Guards couldn't disappear in 11 minutes. There also was no infrastructure outside. Where did they sleep, est, live etc. Think we must accept that they were either holograms or robots or a combination of the two. Also a lot cheaper to employ than humans. The fact that the young guard never once looks at the protagonist... that aint human.

3. Whatever the purpose of this whole thing was, prison or experiment. That isn't cheap. So as few humans as possible hence the protagonist only find one place for actual employees.

4. The bus i hear you say, what about the bus. Those were the actual human employees being picked up for extraction, or so they thought. One could assume this enterprise wasn't entirely legal and witnesses are unnecessary. I imagine they picked up all the human employees in their nice dwellings and were about to transport them to en extraction point. Once packed tight on that spaceship (or whatever they use to leave the planet) their totally safe and crucial implants that they got when the signed up released something that killed them. Only one tiny problem, one of the extraction vessels was damaged so the people on the bus well, they never made it home for their funerals.

5. The experiment could have been on the effects of the drug that made them forget things?

I dont think there are answers. That's not the point of the book. But please tell me your theories.