No, he didn't misread. I think you misunderstood. He is saying that using USB at all, has "overhead". With ext4, it is a journaled filesystem and has its own overhead as well in addition to the USB overhead. Playing via NFS from an ext4 partition won't have the same problem because you are eliminating the USB stack overhead itself. Plus the ext4 journal on the NFS server isn't being updated via LAN - that happens on the host PC which has the ext4 drive.
Either format your USB stick as ext3 or ext2, or setup NFS properly. ext4 is not needed unless you plan to keep the files long term - you don;t need the "journal" of ext4, so go with ext3. You area also talking about UHD/HDR content which has extremely high bitrates. Depending on your USB stick, it may not actually meet the read speed requirements regardless of the OS/filesystem you are using. I prefer to use SD cards in a tiny USB2/3 adapter (aliexpress) - I get much more consistent performance compared to gambling with USB chipsets.
These machines are not high power devices at all and cannot be compared to even the slowest of PC's from the last few generations.
Setup NFS and your problems are gone.