Lasagna noodles on the beach?

While doing a recent beach survey, I noticed this Feather Boa Kelp (Egregia menziesii) washed ashore:

 

It looked quite young — relatively short overall length, with broad blades, and a small holdfast.

When I looked more closely, I was intrigued by the holdfast:  

 

Can you see that the holdfast is attached to a small pieced of wood?

 

It might be easier to see this from below:

 

I wondered about the history of this kelp.  Did it start growing on a piece of wood that was lodged in rocks somewhere and then part of the wood broke off and washed ashore?   Or is it possible the kelp started growing on a small piece of floating driftwood?  Have you noticed Feather Boa Kelp growing on wood before? 

P.S.  I laughed when I read the description of juvenile Feather Boa Kelp on the California Seaweeds eFlora website.  It says they look like lasagna noodles.  A fun description of those broad, ripply blades!