About Thunderbolt 3
MacBook Pro (15-inch, 2016), MacBook Pro (13-inch, 2016, Four Thunderbolt 3 Ports), and MacBook Pro (13-inch, 2016, Two Thunderbolt 3 Ports) come equipped with Thunderbolt 3, an I/O technology that connects devices to your computer at speeds up to 40 Gbps. Thunderbolt 3 combines data transfer, video output, and charging capabilities in a single, compact connector.
The Thunderbolt 3 (USB-C) ports on your MacBook Pro support Thunderbolt 3 devices at speeds up to 40 Gbps when you use a Thunderbolt 3 (USB-C to USB-C) cable. You can also connect Thunderbolt and Thunderbolt 2 devices using the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter at maximum speeds of 20 Gbps. Learn more about Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter compatibility.
from:
Connect with Thunderbolt 3 on your new MacBook Pro - Apple Support
https://support.apple.com/en-us/HT207443
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ThunderBolt-3 is an uncommitted computer port that can do almost anything, with the right cables/adapters. The first cable/adapter you attach specializes the port to one particular purpose, usually a more narrow subset of all it could potentially do. If you connect a USB cable, you specialize that port into a USB port, and it is not at all surprising to find its USB information filed under USB devices.
