$cutright does not "cut from the right" but - as the documentation tells you:
$cutRight(x,n) removes the last n characters of string x and returns the result.
The accidental result with Billie Holiday only works because the part in front of the hyphen is just as long as the part behind it.
Bill Withers has the hyphen at position 14 and if you remove the 14 characters on the right with $cutright() you end up with the string shown in the preview.
If you want to cut the filename so that only the part up to the hyphen remains, then use $left(%_filename%,$strchr(%_filename%,-))