How do you know Unlocked refers to XFR as well?
EDIT: See this slide, much like how the chipset comparison slide suggests that all the things are unlocked in B350 overclocking wise, this slide seems to suggest that a board with X in the name such as the X370 or X300 would be needed to actually get all the features unlocked. Of course it might also be a reference to motherboard manufacturers often adding in overclocking orientated BIOS menu's and better VRMs to higher end boards, with those higher end boards probably having X370 too.