In short, we aren't on track to an apocalyptic extinction, and the new head is concerned that rhetoric that we are is making people apathetic and paralyzes them from making beneficial actions.
He makes it clear too that this doesn't mean things are perfectly fine. The world is becoming and will be more dangerous with respect to climate. We're going to still have serious problems to deal with. The problems just aren't insurmountable and extinction level.
The point was not to imply that shipping is not a large source of CO2, but:
More than once, I have seen it stated that a small number of cargo ships dwarfs the world's car fleet in terms of CO2 emission. This is wrong, and originates with abovementioned conflating of sulphur and carbon.
At 3.9% of all GHG emissions, it is hardly correct to refer to shipping as one of the "biggest CO2 polluters".
It's not low hanging fruit. Moving cargo by sea is really very efficient, and we're not going to reduce that carbon source by switching to other means of transport. The only way to reduce it is to move less stuff.