i don't think this is entirely correct. usb3 uses 9 pins while lightning provides only 8. the exception to this are the ipads (pro?) that support usb3 with this one dongle (not sure which one). those ipads are equipped with a lightning port that has 16 pins (8 on one side, 8 on the other). all iphones to date with lightning, including the latest 8 and 8 plus, only have 8 pins. and as mentioned above, none of the cables with lightning connector on one end have support for usb3 because they only contain 8 wires for those 8 pins.
here's a quote from
changguangyu where you can see the difference in the number of pins in iphones (left pic; 8 pins) and usb3-ipads (right pic, 16 pins):
unless apple uses some fancy non-usb-compliant trickery to get usb3 out of 8 pins/8 wires even though the standard uses 9, or unless they equip all iphones and ipads with those 16 pin ports AND start producing appropriate 16 pin/16 wires cables, we are still stuck with usb2. i wonder if the iphone x will feature usb3.