It could have reached number one because of Boukenger -- don't underestimate the power of Yasuaki Kurata!
I remember reading the same thing happening in '03. The double bill that year did really well, but for Abaranger, as viewers were bailing on snoozefest Paradise Lost. People could be bailing on GSL, too...:shrug:
The site you linked only seems to go back as far as 4 weeks ago, however it does list the previous position as 4 on the week of 8/12 and the previous week was the premiere. So obviously Kimiden didn't check his sources. Someone better make a retraction.