Paddy Layback
N/A
I would suggest it is not if you can safely navigate around it.
Yes, I see what you mean, but:
He might be seeing it clearly, and able to navigate around it, when he is: wide awake, engine working, well crewed, in light weather, in daylight, with no tide to catch, at slack water, etc etc.
And he might rightly take a view that the pot buoy in question would present a potentially lethal hazard to navigation, should any of those ideal conditions not be present.
(In my life they are never all present..)
In which case, removing it (if he could do safely) would be a public duty, like removing some barbed wire stretched across a cycle path at neck height.