What sort of squeegee was it? If it was brass, I'd be very surprised if it was the squeegee that scratched the glass, as it's too soft.
On any building site you can see stacks of windows waiting to be installed. I've sen them being dragged across each other with all sorts of debris in between them, resulting in loads of scratches. They still go ahead and fit them in the hope no-one will notice. Then lo and behold, salvation arrives in the form of the poor unsuspecting window cleaner - lucky builder!! Wait till he's cleaned the new glass then point out all the scratches "he's just put in the glass"
I don't do builders cleans for this and various other reasons, but when I did I soon got wise to this one, and always looked first. Any damage was recorded and reported to the site agent before I started work.
There was always damage of some sort, usually scratches, which I would have got the blame for if I hadn't been careful