You're getting taken in by a misdirection.
>for them to run different software than they say they do.
They don't even need to do that. They don't need to do anything different than they say.
They already are saying only that the data is kept private from <insert very limited subset of relevant people here>.
That opens the door wide for them to share the data with anyone outside of that very limited subset. You just have to read what they say, and also read between the lines. They aren't going to say who they share with, apparently, but they are going to carefully craft what they say so that some people get misdirected.
They're not doing that because it's obviously illegal. GDPR forbids sharing data with unknown other people.