Both ALAC and FLAC the same file, they are identical. Flac was was obtained from ALAC in EZ Audio Converter 10
Edit: Removed link to example file
Media info shows 24 bit of ALAC, mp3 tag shows 16 bit of ALAC. After cverting to FLAC mp2 tag shows 24 bit. It is also strange that the size of flac is less than the size of alac

I have few more ALAC files from the same source & label with the same problem if needed for example. Other ALAC files frome this source & label are OK
How exactly did you define the column B in Mp3tag that shows 16 for your m4a file?
JFYI: Exiftool also shows 16 for this m4a file:

Mediainfo shows:
It's probably just %_bitspersample%
The file headers state 16 as sample size, after copying to a new file via
ffmpeg -i input.m4a -codec copy output.m4a
the output.m4a also shows 24 bits. It's probably an error in creating the file. Other tools might decode parts of the file to obtain actual sample size.
Bits сolumn %_bitspersample%
I think metadata in files m4a (ALAC) in itunes store is corrupt