It is ironic that you point that out. I would not have corrected him had he misused 'who' (i.e., if he had used it for the objective case) -- that would have been a little 'less wrong' than using the supposedly dated 'whom' for the subjective case, as others have said.

That said, I didn't want to be rude or impolite. To lessen the impact of the statement, as to make it 'just a side note!', I enclosed it in parentheses. But that seems to have done little good, since it has ensued another discussion of its own! Oh well, I hope someone out there maybe learned something interesting. :)

Cheers!