Unless he was talking about Duel Wielding Roxas himself. Keep in mind that the novels had Roxas Duel Wielding at a time before the end of Days - thus this comment too arguably is rectonned out of any semblance of canonity.
Actually, the novel he's talking about was choc-full of hints towards Xion and Days; it was written in May last year, when Days was well underway, by Kanemaki herself, who was working on the game.
Many mysteries from that novel were explained by Days; the envelope Axel carried
had the winner stick in it, Axel wondering about his 'hazy memories' was about Axel
forgetting Xion, Saix asking Axel about his 'wound' was about Axel's
fight with Xion.
So, it wouldn't surprise me if this was related to Days, too:
Axel--Seven Days said:
Just then, a change came over the keyblade-wielding Roxas.
"Two?!"
Roxas gripped a keyblade in each hand.
I think I've seen one of those keyblades somewhere before. But, I can't remember.
He seemed to be remembering something--but, as if shaking that off, Axel flashed a grin.
Note how he's 'remembering something'... probably a reference to Xion. Not that these are canon, anyway.
And, as for 'novels having Roxas dual weilding before canon', are you sure you're not referring to that mistranslation of the short story in the booklet that came with the limited edition of Final Mix+? An old fan translation said he had keyblades in his hands, when I looked at the original, I pointed out that in Japanese they don't have plural form of nouns, and it could very well have said hand OR hands. Anyway, that old thing got COMPLETELY retconned into nothing by other plot-related points. A shame, it was cute ;o;