SOG (sea of green) Is a method of growing where you usually start with a mother plant (mother plants are used to butcher down into cuttings), or you can use seeds, but it's less economical.
You generally plant the seeds/cuttings into small pots since your not going to need too much root space.
What your doing is only letting the plants go through the vegative cycle for a short time. This is accomplished by cutting down the light cycle from your origional vegative cycle of anywhere between 16/8-24/0(light/dark), down to 12/12 and a change in nutrients helps to initiate the flower cycle (thats when you get buds).
You want the plants to be small and uniform is size because your gonna end up with a shit load of em' which means that they are gonna get very good lighting, and you dont have to let the plants vegetate long if at all, your choice.

So to answer your questions, yes it does stay in thwe 6 in pot it's entire life, you want many small plants that will yield around a joint a piece.
No the pot dosent stun the growth, you just go into flower early on so it dosent get very big, if you had a plant in too small of a pot it would get what is known as root bound and die.
3-6 months in a 5 gallon will grow big plants (my growing preference) they get big because the extended light hours durring the vegative cycle lets the plants get big because they know winter is not gonna come soon. They start budding when you lower the hours of light to 12/12 because they think that winter is coming which they dont like, so thet produce buds to reproduce (basically they want to fuck so future generations of thier species can live on)

I may have confused you so feel free to ask more questions, me or someone else will try to answer them for you.
peace