I did spend about 20 minutes looking into this, it seems that there's an (admittedly undocumented) IOCTL which is in the Winsock headers (MSWsock.h) called SIO_EXT_POLL which seems to just use the poll device IO control code and so they could probably do this without messing with low-level AFD weirdness.
That said you'd think with Microsoft going all in on Rust, last I heard at least, that they could find a way to re-implement this code correctly. Hell, if they at least documented the IOCTL they could probably get co-pilot to do it for them ;)