Nah, he very obviously read the issue of Uncanny where Kitty takes what she thinks are Peter's ashes back home to Russia, since he refers to it directly. He also seems to have read enough of Ellis's Excalibur to have gotten the memo that Kitty is good in a fight.
To my mind, it's fairly simple. Whedon was and is into Kitty/Piotr, whereas most of the X-fans on the Internet these days are Kitty/Pete fans. Whedon wrote what he liked because Marvel handed him the keys. I don't think he regressed Kitty as far as some hyperbolic fans like to pretend he did, since Kitty is at least talking her feelings out with Peter like a reasonably mature individual would: point-blank, only as much equivocation as is needed for her to get her mind around what she's doing. Whedon's Kitty is not the thirteen-year-old that fandom would pretend she is; she's a young adult.