If you open the file as utf-8 you will see "ö" and if you open it as MacRoman you will see "√∂". You could also open it as Traditional Chinese or Simplified Chinese or many other things and see other things. UTF-8 byte order is always the same, so there is no need for a BOM, though some editors might use it as a hint.
Given that his editor seems to have interpreted the file as utf-8 with the BOM in place and as something else without the BOM, we might guess that his editor recognizes the BOM.
We could also, of course, guess that his login account is set to default to something other than utf-8, which is also in keeping with my experience with Mac OS X when the user has not deliberately messed around with things.
