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.
I don’t recall seeing anyone saying that 1.5 degrees warming was an existential threat to humanity. That said, its already killing some humans at less than 1.5 and that will only get worse