Saturation vs Gamut

I was looking at the scopes (in DaVinci Resolve, i think they are more or less the same in  other softwares)  of frame of the famous coin scene of No Country for Old Men and i noticed something i can’t understand. Vectorscope tells me the color are quite muted and saturation is low, but the chromaticity shows a rich variety of colors, almost filling the Rec709 gamut. If i reduce the saturation the gamut gets smaller, if i increase the saturation it gets wider, so it responds to saturation, not just variety of hues. But how the two things (low saturation and wide gamut) can stay together? The answer i gave to myself:

1) it’s a DaVinci issue

2) it’s because the frame is a simply screenshot from Youtube, it messed up things somehow

3) who cares, just consider the vectorscope, the gamut is just for broadcasting check and it’s not that relevant for my purposes

4) Rec709 gamut is actually way smaller than i think, once showed in the vectorscope

5) Roger can break laws of physics

I think it’s answer 4 (the gamut is actually quite small) , even if i suspect it’s answer n.5 , and in any case i know that vectorscope is more useful than gamut (for what i need to do), but still i’m curious about the motivation of this apparently strange thing.  Thanks in advance for any explaination!

Don’t pay attention to the distortion of the frame aspect, i  resized to fill the DVR window and avoid the black letterboxes.