Exactly. Not only this argument makes no sense, but it is also based on nothing. There is no news, rumors, or reports which suggest that MS wanted to order more wafers but couldn't afford it.
Usually companies bid for these types of things. Microsoft probably didn't want more wafers because they didn't think demand would be so high. Plus they are splitting them between two systems which would lower the amount of each in the market.
Sony probably predicted really high demand for the PS5 so they bought more wafers to try and meet it. I have a feeling they won't he able to meet demand for quite a while though which sucks for people trying to get one.