It would certainly be good if AucTeX recognized that file as a LaTeX file. It would be a simple fix to add PassOptionsToPackage to a list of commands in the function tex--guess-mode in tex-mode.el (Maintainer:
emacs-devel@gnu.org).
For what it's worth I still think it would be really good if AucTeX was merged into Emacs. Let's avoid the feeling of "when you use Emacs you really should first customize it like this and this and this". When I use Emacs in demos for students I use a plain no-frills Emacs, because I want it to be what they get themselves if they install on their own computers, but I've "had to" make an exception for TeX, because not using AucTeX would be too hard for me.