Which statement takes priority over the others?
Is it the one made in the guidebooks that say his final attack can obliterate a star, or is it the one that mentions the ability to destroy the planet (anime) and the planet's surface (manga)?
The manga is the primary source material from the anime was based on as an adaptation (and the guidebook is based on the adaptation instead of the manga), so what is mentioned in the manga would take priority here.
ONE most likely intended for that feat from Boros to show that Saitama had the power to easily blast through planet razing attacks, which would have placed him solidly above every other hero in the association at the time of that chapter's release.
It was strong enough that Saitama was willing to show off the power of his serious punch for it so Boros' final attack should be a benchmark for top tiers in the verse more or less.