According to their slides from WWDC last year, it also offers TCP in userspace.
[0] https://devstreaming-cdn.apple.com/videos/wwdc/2017/707h2gkb...
I am not doubting they have some sort of user-space TCP implementation. I am trying to understand how much of TCP they moved out of the kernel. From what I can gather they still have enough of it in the kernel such that the related syscall/uIPC overhead does not allow more than the 30% performance improvement announced.