After quick investigation, here is what that had happened with Dire Wyrm.
On the old classic chronicles it has only silence SB (WC did not have Chant of Movement back then) in the drop - https://web.archive.org/web/20150620021157/http://l2central.info/classic/Жуткий_Змей .
Then after update and introducing chant of movement, they changed drop for Dire Wyrm - https://web.archive.org/web/20160604003139/https://l2wiki.com/classic/Dire_Wyrm .
So, since we have both SBs - Silence and Cancel, in the Wyrm's drop, I assume here they just combined drops from both updates.