Find files containing string in file name and different string within file?

That's because grep can't read file names to search through from standard input. What you're doing is printing file names that contain XYZ. Use find's -exec option instead:

find . -name "*ABC*" -exec grep -H 'XYZ' {} +

From man find:

   -exec command ;
          Execute  command;  true  if 0 status is returned.  All following
          arguments to find are taken to be arguments to the command until
          an  argument  consisting of `;' is encountered.  The string `{}'
          is replaced by the current file name being processed  everywhere
          it occurs in the arguments to the command, not just in arguments
          where it is alone, as in some versions of find. 

[...]

   -exec command {} +
          This  variant  of the -exec action runs the specified command on
          the selected files, but the command line is built  by  appending
          each  selected file name at the end; the total number of invoca‐
          tions of the command will  be  much  less  than  the  number  of
          matched  files.   The command line is built in much the same way
          that xargs builds its command lines.  Only one instance of  `{}'
          is  allowed  within the command.  The command is executed in the
          starting directory.

If you don't need the actual matching lines but only the list of file names containing at least one occurrence of the string, use this instead:

find . -name "*ABC*" -exec grep -l 'XYZ' {} +

I find the following command the simplest way:

grep -R --include="*ABC*" XYZ

or add -i to search case insensitive:

grep -i -R --include="*ABC*" XYZ