He might have been metering the sky to put it at about +2 and keep it from blowing out.
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But wouldn't that make us too dark?
Yes, it would if the contrast range was too great. But the alternative, giving adequate exposure to the foreground, would blow out the sky. The best compromise is to expose so the sky is overly bright, just short of clipping. This also gives the foreground the most exposure that is possible without losing the sky. As shot, neither will be satisfactory but both areas will have the best possible data for post-processing. In situations that are beyond the abilities of the camera you have to expose in a way that will give you the best starting point for PP. Of course, this is best done in RAW.