The radio buttons for 'Order by' are not inside a radio group and are not associated with the 'Order by' text (which should be the name for the group).
Just to provide a bit more detail, the fieldset/legend approach isn't really viable as it stands, but the role/aria-labelledby approach should handled equivalently.
Accessibility resources free online from the international standards organization: W3C Web Accessibility Initiative (WAI).
www.w3.org
We use radiogroup for radio rows and group for checkbox rows automatically now, so this will catch many places though not all. As it stands, I think that can be tracked in one of your other bug reports, because the conceptual issue there are complex form rows where we can't automatically connect the control to the label.