Hello Aniduan,
Thanks for taking the time to point it out. But it is not a typo.
The number of ultimate entities comes to 82 with Nibbana.
However, “The 81 “basic units” that make up this world are one pure citta, 52 cetasika, and 28 types of rūpa.
– Thus, 81 refers ONLY to “this world.’
– Nibbana is NOT in this world.