I mean, it's an EU-funded academic site designed to raise awareness of privacy issues, so I'm inclined to believe them when they say they aren't keeping any of this data.

Maybe it's because programmers tend to think categorically, but I find HN frequently has this problem where people are freaking out like "why is it okay when Mozilla does X but you don't want Google to do X?!" as though we're supposed to treat every question as some sort of sui generis scenario divorced from all history and context.

History matters, context matters. I (generally) trust academics and democratically-elected governments, and I (generally) distrust giant ad-tech companies and authoritarian states.