The site states that B0 "sustains" spin precession, but does not create it.
Isn't that a strange way of putting it? i.e. if B0 does not create (cause) precession, what does?
Good philosophical question!
Consider the following metaphor/analogy of the sun and a seed. The seed intrinsically contains essential DNA and nutrients for life, but only when warmed by the sun will sprout into a plant. Does the sun create the plant, or just sustain it?
The nucleus has an intrinsic property (spin) that exists whether or not an external field (Bo) is present. Only when Bo is present does precession become manifest as a measurable/observable property.
I'll think about doing a little rewording of the question to make this clearer.