I think that is nonsense. ftp'ing it non-binary would insert a carriage return character at each linefeed, thus corrupting the file completely. But you can try ...
I just had another idea -
There is a weak chance that it could be a gzip'ed file. Do you have gzip/gunzip installed?
If yes, you could rename the file from file123.32 to file123.gz , issue 'gunzip file123.gz' and see if it works without an error message.
If so, issue 'file file123' again and examine the result.
If you don't have gunzip, get it here -
http://www-03.ibm.com/systems/power/software/aix/linux/toolbox/download.html
Click 'Alphabetically ..', locate 'gzip', click 'RPM' to download, transfer to AIX and issue 'rpm -i gzip-1.2.4a-10.aix5.2.ppc.rpm' in the directory containing the downloaded file. gzip/gunzip will then be in /usr/bin.
As I said, a weak chance, all the more because your vendor didn't mention gunzip.