This is totally incorrect. Individual options contracts are indeed written against 100x of the underlying asset but this has absolutely nothing to do with the relationship between the price (premium) paid per contract and that of the underlying share. To given an example, you could find a put option whose premium is actually equal to the current market value of the underlying (i.e. a merely 1 to 1 relationship) or one that's so far out of the money that it's a 1 to 1000 relationship. Without knowing more details about the precise options SoftBank bought, we cannot infer how much market cap in underlying shares the $4bil corresponds to.