I don't think Konami ever said it was there. Developers and publishers usually don't make claims like that unless it's something they're putting in the ads or on the box. I guess it could be in the instruction manual, or in a guide if one was published for this version. I doubt it, though. That is, it wasn't in the manual for the PS version, so it'd be weird to document the feature ten years later. And I very much doubt they'd have done anything other than re-release the PS guide, assuming there was one, and they felt like a re-release would sell.
I don't think it's explicitly stated on this site that the stat stones are exploitable. The exploit probably wasn't checked because it didn't seem particularly important, and it's just taken as implicit that it's still there because the guide says, "no bugs aside from the Matilda Glitch were fixed," or words to that effect. We don't even know that implying it's there is false yet, because nobody has done the work to confirm.
As to how such a theoretical mistake could have been made, well, not many people in the West were that interested in this remake, and similarly few people have your weird, laser-focus on getting correct information about a trivial mechanic in a remake that maybe a few hundred people outside Japan have played. That focus would be admirable, if it didn't also involve constantly harassing other people to develop the information for you.