Do you get the expected behavior under emacs -Q? It's possible you've disabled case-insensitivity.
Without knowing your arguments to find-name-dired (you should add them to your question) it's hard to say. If you included the double quotes, Emacs will escape them and find will look for files that include them. Based on your output that ...
My solution is way too hacky:
A file that you want to have Imenu to access is likely to be tracked by Git.
Use find-file-noselect on all those files (I don't know how to detect binary files with Emacs so limiting on VCS-tracked files is better), and accept the risk of hooks and advices, auto-loading functions, etc.
@phils answered the question. This is just to say that the version of find-grep-dired in library find-dired+.el provides a bit more than the vanilla version:
It has two optional args, DEPTH-LIMITS and EXCLUDED-PATHS.
The interactive spec uses read-from-minibuffer, read-file-name, dired-regexp-history and find-diredp-default-fn.
find-grep-dired is an ...
The following does that and presents the results as a dired buffer:
You'll also want to know about:
(which doesn't support the -l option to grep, but is usually what I want from a recursive regexp search.)
Looks like you are accidentally using the MS Windows find command.
You need to have a UNIX or GNU/Linux find command (and grep command). You can use Cygwin, for example. Or if you have such a command available already then you need to put such programs in your PATH environment variable.
See this Emacs Wiki category page for links to wiki pages about ...
You can try elgrep.
The github version linked here already has already an option for case sensitivity.
Within a day or so that version should also be available via list-packages from melpa.
Menu for specifying search strings and search options with history and M-tab completion.
elgrep does not depend on the external grep tool