Cheers Tim
Yes, you're right, the bit I missed was when the instructor on the video was metering off the grass, he zoomed in so that the grass filled the frame and yes, as you say, spot or partial.
As for the actual zones and how they compare to the camera's meter here's an explanation for anyone wanting to explore more. I apologise in advance but it is taken from Mr Rockwell

and is based on film, but the principle still applies to digital. I think it's a nice easy explanation that eases people into a more detailed one as in this link
http://dpanswers.com/content/tech_zonesystem.php
Edit: crossed post with Tim
I'm not going to diss the Zone System because an understanding of tonal value is very useful, but with digital, that's about where it ends.
The Zone System is for shooting
negative film and includes both exposure setting and individual development and printing techniques. Where it differs from digital, crucially, is that neg film is very tolerant of over exposure and highlights are always retained even though they block up and some detail is lost.
Digital is just the opposite and when you over expose the highlights they blow into nothing. It's like slide film in that respect, but the difference with digital is that you can make adjustments in post processing which you can't with slide film (if you like, shooting direct to JPEG is similar to slide film).
For optimum exposure with digital, the technique is to shoot Raw and push the Exposure To The Right of the histogram, and then pull the tone values back to their correct positions in post processing (good article here
http://www.luminous-landscape.com/tutorials/expose-right.shtml ). Generally speaking, if you just put Zone V on zero then the highlights (at least the ones that matter) will often not even reach the right hand side of the histogram and you will waste a lot of potential. Futhermore, the sensor is able to record far more data on the right than the left - very substantially more.
The end result of ETTR technique is usually an exposure that is a couple of stops more than the meter will suggest, with maximised and extended dynamic range. Highlights and mid tones are finely detailed, and in particular the shadows are dragged out of the murk with better gradation and much less noise.
You don't need to know anything about the Zone System for ETTR. You just need to be able to read the histogram and with blinkies enabled (highlight over exposure warning, in the menu) that is pretty straightforward. Take a test shot and chimp. Increase the exposure until the blinkies start to flash, which they will do quite soon on shiny spectular reflections like white paint, car bumpers etc. But that usually doesn't matter as they will blow anyway, wait until things like white cuffs and collars start to blow, reflections off foreheads etc. You probably want to retain some detail there, so that's your limit.
When the blinkies
just start, you are close to the limit, but not yet over it. However, also bear in mind that blinkies are derived from the JPEG image parameters, as are the LCD image and histogram, and the contrast setting in particular has quite a big influence on that, like one stop or more. It you really want to live on the edge, turn the contrast down to zero and that will allow you to maximise the result.
When you get ETTR right, it looks brilliant. Images have much more richness and punch. But you have to know what you're doing and be able to make a good judgement call on which highlight areas you are prepared to let blow (either because they will anyway, or is doesn't matter) and which ones to hold. Different cameras/settings and processing regimes will behave slighly differently, so do a few tests.
If this sounds like 'expose for the highlights and let the shadows look after themselves' technique, it is effectively exactly that, and there are other ways of doing it, eg spot meter off a key highlight tone and position that accordingly - which TBH is basic Zone System practise

The difference is that it is customised to your camera and your way of working, and IMHO it is also easier and more accurate.