(I'm curious why they singled out GPL version 3 specifically though.)
Because it isn't an anti-free software thing, it's an anti GPLv3 thing. You see you can't have one single app store and have GPLv3 compatibility, it's the same with Apple's app store.
Free software is fine, it's just that some free software licenses conflict with the idea of a single controlled app store.
Free software is fine, it's just that some free software licenses conflict with the idea of a single controlled app store.