I’m not sure which part of ‘boil the oceans’ you think we can sort of exist in. In this scenario we become Venus except with thinner atmosphere, so no balloons to save us.
While such a scenario is certainly possible, it's not something that can be achieved by humanity by solely leverage on its current capacities to transform earth environment.
So, to answer your question, in the part where humanity can certainly change the world to its own detrimental, but is currently not able to really put it in a state where absolutely no life form is conceivable anymore, and that even putting it a state where some hunters gatherers would not be able to survive is not a 100% garantie outcome of current trends. though I would rather consider the current trend rather awful if you ask.
They're not saying we can exist. They're saying that it's not uninhabitable to something, therefore making the value judgement that it would be uninhabitable is simply not true. Which is another kind of value judgement about how important your own values are.
