Install WIndows 10 on USB-C flash drive
As far as I am aware Boot Camp asks that you create a bootable USB flash drive to install Windows on your Mac.

Though I don't have experience with a USB-C MacBook Pro, USB is USB, differing only in speed and the type of connector. MacOS should not care what kind of USB key you have.

You will have to download the Windows 10 ISO to your MacBook Pro so Boot Camp can use it to create the bootable media but other than that it should work fine.