I have that book too but after having read many other books about the Bataan campaign, I've come to the conclusion that that was a localized decision to exchange weapons. Maybe here and there someone would exchange rifles but it certainly wasn't wholesale. There are too many accounts of the last days in Bataan where there were mentions about the garands they carried in battle.
I've even come across an account where some young soldiers didn't even know how to work bolt-action rifles because they went to boot camp and were trained with the garand in 1941. These were the young and non-prior service soldiers and the garand was the only rifle they knew.
By the way, here is a LIFE Magazine photo of a soldier in Manila before the war started:
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