Just because the PS4 box says 105 GB doesn't mean it's going to be 105 GB, what's printed on the box shouldn't be taken as gospel. That copy was almost surely based on a conservative estimate given at whatever time the box design had to go to print. This kind of thing happens all the time - remember how the original No Man's Sky boxes had online/multiplayer info printed? Printing requires lead time and things can change by the time something gets released.
What about if it says it on the digital store? lol