From Painius:

i sometimes find it difficult to envision
the strong nuclear force as being
ultimately accountable for the Sun's
massive magnetic field that reaches well beyond the orbit of Pluto!

There are certainly other mechanisms that generate magnetism, such as
the geo-dynamo within the Earth. An on the sun, those great looping
prominences are clearly spinning 'flux tubes' generated deep within the
sun. With the sun so robust magnetically, it's not surprizing its field
should reach 'way out thar, i would think.
Anything that'll impart a spin component to a spatial flow
will produce magnetism, not just the strong force within atomic nuclei.
oc