Both theories sound good, and given that it’s Pixar, there’s definitely a reason for such a seeming non-sequiter of a response. At this point though, FONY’s theory sounds reasonable (figures his will would be in his office)
I think of it the same way as A113. Remy asked something which the figment of his imagination couldn’t possibly answer. Not just because of what the line is but how it’s delivered. It makes me think as if you were talking to someone with some sort of mental handicap and one second that person is on topic and then suddenly they say something about pink elephants at the zoo.
Actually, to be fair, Remy didn’t know it was Guesteau’s office. He’s probably never been in there much, conidering Skinner is most of the time (plotting new frozen food products). Sure, Remy could’ve placed two and two together, but as the line he throws us “a cook’s work is never done”
And since this Guesteau was a figment of Remy’s, it wouldn’t have know the answer. And the surprise we see of the announcement only benefits the theory. This Guesteau Remy, in small terms, “made up” as a companion when he had none. So it didn’t retain knowledge Remy himself didn’t have, and that extends rather well as it reminds Remy that he never pretended to be a rat/chef.
it probably said what Remy was thinking. “…filed with your will?” and Remy could be thinking “this is Skinner’s office…used to be Guesteau’s”. So in his head, projected kind-of as Guesteau, was reminding him.
Gusteau only knows as much as Remy knows.
Upon Remy discovering Gusteau’s Will, that’s when Remy finds out it used to be his office, and then directly after that’s what comes out of Gusteau’s mouth because that was what popped in Remy’s mind.