Also apple makes decisions like encrypting binaries and then compressing, removing a lot of over the air space savings. They don't give free apps the option to just sign their apps and not encrypt them for smaller IPA sizes.
I wouldn't be surprised if a similar decision was made in the xcode toolchain that caused a similar issue.
I'm skeptical Swift creates significantly larger binaries, let alone 3x-4x, but I'd still use it if so. Using optionals and stronger typing is makes it easier to write correct code, and anyway we can save users from wild pointer crashes is super valuable. Far more valuable than the cost of a couple megabytes of code in an ocean of PNGs and Cocoapods.
All other things being equal, a swift app is much larger. The article also is just talking about binary sizes, not about all the other graphical assets.
You'll also be surprised how much stuff is reduced in swift 4. Swift is still in beta, lots of low hanging fruit to improve still.
Is compression not the first step of basically every encryption algorithm ever?