So, I would take these promises with a few grains of salt. For the purpose of improving their product they actually need to know how people are using it. So, they have to balance quality of their product with privacy. More privacy means their engineers are not getting all the information they need to do the best that they can. And they are competing with companies that are not holding back on that front. So, there's a bit of tension there.
Of course the fact that it's a paid product, allows them to make some stronger guarantees and build in business friendly wording into their terms of use beyond just promising that it's all fine. The flip side is that you have to sign in to use the product and prove that you paid for it. So, you can't use it anonymously.
IMHO, they should target the SAAS market and offer to make stronger guarantees to companies that are legitimately worried about their intellectual property leaking via search queries. Having people happily dump whatever in a Google query actually potentially gives Google a lot of insight into what these companies are doing. Including their direct competitors. And I'm sure they solemnly swear that they'd be doing no such thing but the temptation to tap into that is probably enormous for them. I can imagine a few companies that would pay a premium to cut off that particular flow of information. Those per seat deals that get sold by the dozens/hundreds are potentially worth a lot. B2C sales is a lot harder than B2B. And of course access to services like this is also a nice perk for employees.