Firmware shorts IO pin for USB OTG devices?

https://github.com/arduino/ArduinoCore-samd/blob/020b419fc1dbca49b23b7c0b5e47d50fb2a04485/cores/arduino/USB/samd21_host.c#L145

This code sets PIN_USB_HOST_ENABLE high - but looking at the MKR WiFi 1010 schematic, it's also connected to the USB ID pin. In USB cables, one end of this is tied to GND.

It feels to me like:

1) The board was designed so that PIN_USB_HOST_ENABLE was intended to be an input?
2) Writing it high means that when a cable is inserted, it's grounding an output thats high

Kind of related to #440. I'm just trying to work out what the deal with this pin is. When I try to write it LOW on my board, the IO only goes to 0.3V, not 0V, and the OTG pin on the power IC rises to just 0.1V, when I'm trying to make it go high.