To be fair, it was out of the top 100 on the montly charts in September and August typically sees slow sales.
I really hate using Amazon stats this way (too in depth) but I'll do it anyway to just make a point.
Xbox One in August did around 202K. The Halo 5 bundle was the top Xbox One bundle on Amazon's chart but it didn't count for that month (obviously). The second Xbox One bundle on the list is the MCC bundle.
The MCC bundle was #40 for August. The Halo 5 bundle (which again, didn't count for August) was #24. If Xbox One did 202K in August for bundles that actually counted, then what does Halo 5 bundle's position say about how it did during the same month? 50K (added to October)? 100K (added to October)? It was 16 places above the top ranked Xbox One bundle that actually counted during that month.
Hence why I feel we can't really deeply look into October's Amazon stats. Not really showing the whole picture at all in my opinion. I do feel though that October will be close thanks to PS4's price drop (and still haven't posted a prediction yet due to it).