The rule of two be damned.
A Sith who just coincidentally happens to be there... Compared to Dooku's boss?
Even if Anikan thought that Palpatine was Dooku's apprentice, that put some serious bifurcating in Anikans reasoning that he joined the separatists at the height of the Clones Wars... More so than he just met a kindly old Sith who convinced him the Jedi were crap.
This book was put into print and approved by Lucas.
Someone on the ranch agrees with this silly point of view.