The book is correct. For the reason why level 6-9 spells exist for the Warlock when their Pact Magic slots cap at 5, check the Mystic Arcanum class feature on PHB p.108.
At 11th level, your patron bestows upon you a magical secret called an arcanum. Choose one 6th level spell from the warlock spell list as this arcanum.
You can cast your arcanum spell once without expending a spell slot. You must finish a long rest before you can do so again.
At higher levels, you gain more warlock spells of your choice that can be cast in this way: one 7th-level spell at 13th level, one 8th-level spell at 15th level, and one 9th-level spell at 17th level. You regain all uses of your Mystic Arcanum when you finish a long rest.
It's simulating the once-a-day spell slots that other casters get (presumably, they didn't want you recasting a 9th level spell every time you rested throughout the day), but there are a few minor differences.
- It's not technically a spell slot for anything that cares specifically about spell slots (such as the feature below that in the PHB, Eldritch Master), as mentioned.
- Unlike most spellcasters, you only ever "know" (as an arcanum) one spell each of 6th-9th level.
- You cannot 'upgrade' spells to those 6th-9th level 'slots', as they aren't really slots. You always cast the 6th level arcanum at 6th level, the 7th level arcanum as 7th level, etc.