Facts:
Iruini and others think Keetongu is a myth.
Sidorak’s species hunted Keetongu’s species until only Keetongu remained.
Sidorak says “but Keetongu doesn’t exst!”
Keetongu can cure the Visorak victims
Theory:
Sidorak finds out that Keetongu’s species, a rare little-known species, can reverse the effects of Visorak venom (or maybe just Keetongu himself), and tries to kill Keetongu and wipe away all memory of their existence. He kills all but one, kills all who know of them, and destroys all records of them. Sidorak knows Keetongu is real, but denies it. Then Keetongu gets revenge by killing Sid.