In lack of any evidence, you can and actually must rely on your priors. There are things that were a-priori unlikely but are still considered true. However, we believe that they are true because solid evidence has been provided to override our priors. In the present case, there is no such evidence.
Sure, but the title isn't "LaMDA is probably not sentient", it's "LaMDA is not sentient", and there's no definitive proof of that.
There is no definite proof that my shoe is not sentient but… come on!
Why is this so outrageous? There's some lines of thought in philosophy of the mind that propose that conscience is a fundamental property of the universe and every particle is sentient to a degree.
Up until now, we can't prove anything because we don't really know how to define nor measure consciousnesses.
Yes, and if you had written an article claiming that your sock isn't sentient and presenting "just look at it!" as proof, I'd say what I said here as well.