I think that Rich has simply seen that there is no simple USB port on the E373, and that presumably youd have to use the USb A to B Host port to transfer anything.
Back in the day, this was also the ONLY way of transferring files back and forwards between my old Tyros 1 and a pc.
OK it had, a Floppy Drive, but it was often quite a long process to transfer much at all.
I got round it by installing a laptop sized Hard Drive. Simple process turn the Tyros over, undo the 8 screws, remove the hard drive holding cage,and then I could transfer away to my hearts content every 3 months or so just by connecting a simple external ide to USB cable to the USB on my PC,
You'll of course, wonder why I didn't use the USB to HOST socket.....Well I couldn't because at some point it got fried during the file transfer operation, and despite attempting to get somebody to replace the circuitry, the best price I could get for a repair was £350. Then Covid came along, and the guy who used to do those repairs just dropped out of circulation completely, so I sold it as it was
It's also the reason why I will never, ever, ever again, connect any keyboard directly to a computer.. I don't like or trust those USB Printer socket shaped Host connectors....too much to go wrong, as I found out.
A USB Memory stick is pretty bombproof.
That's why I suggested the method above. But I am really and totally amazed that a keyboard this new would not have a dedicated USB port.....Come on Yamaha... Stone Age stuff..