Khan's memories of the Nak language were older than his tragedies. He was still in Ylaco's training camp back then, but Professor Thogett's xenolinguistics class had already given him troublesome clues.
Even before learning the Niqols' arts and transforming, Khan had confirmed that he could understand the Nak language. He didn't need studies or experience for that. His brain instinctively translated those seemingly meaningless sounds.
The same had happened with the Tainted animal, but Khan had reason to be surprised anyway. The fact that a monster seemingly evolved from mere beasts could speak that language was shocking. Yet, there was more to it.
The monster had used the same words from Khan's nightmare, which the scientists had also reported. He already didn't believe the matter to be a coincidence, but that event dispersed his last doubts.