As the reason for using a polarizing filter on an enlarger must be quite arcane, wouldn't it be better to ask the fellow directly? (And then get back to us. )
If only I could unfortunately I cant but I can say he was one of the countries best mural printers. I was 23 when I worked along side him. I would say hello to him every day and all I ever got back was a nod of the head if I was lucky, he was notoriously quiet but technically brilliant. He knew every intricate function of the enlarger, The polarizing filter was no joke and it wasn't used for all prints but I'm still stumped as to what it was for. Shrugs guess I will never know.
"Its my profession to hijack time" ~ Stephen Frizza.