No idea but isn't it great!

My guess is this must have been a flower stalk at one time, and is now a seed stalk. With a little moisture, some of the seeds have sprouted prematurely.

Its a case of fasciation - happens occasionally on quite a lot of plants for various reasons like cold, damage, a genetic blip in the DNA in that stem. Just cut it off, the plant should be normal next year.

I agree its a form of fasciation. Lupins produce pods that are 'explosive' and through the ripe seed a metre or more away from the parent plant. So they wouldn't germinate in the pod.