I have to admit, I didn't get this the first time I read it years ago - and I still don't.
Since the heading of the Cessna to the Sun was 274 degrees it was greater than the 270‑degree heading of the DC‑10, that meant that the Cessna was south of the DC‑10 as shown in Figure 20.
Different elevations dependent on longitude yes, but 'heading to'.
PS. I can already feel that I may regret posting this.