Experimental behavior manipulation, without even telling the subject they are part of a manipulation experiment? You would be chased out of the room and your reputation destroyed! Utterly unacceptable. But in webdev universe this is somehow seen as a totally normal practice.
Seeing as they were posting the backlash on Reddit, I'm guessing a lot of people downloaded the app to log in and Reddit said "Big Success!" when they checked the stats.
The GDPR's notion of informed consent really needs to be applied pervasively to all kinds of consumer contracts. If it's hidden in walls of text that the average user doesn't read it shouldn't count as consent.
But the real solution is better web page design.
For me, I use google so often that I can rapidly parse information without really needing to read much of the text, the link just sort of 'looks' right. I've observed my wife reading google results and she is much slower and more methodical, probably because she doesn't google things 20+ times a day every day like I do.
That's how I end up misclicking, because i'm not working at the speed of a normal googler.
It is really annoying though, there are some css tweaks you can make using browser extensions to make that disappear if you're so inclined.
A horrific piece of UI/UX/engineering/whatever.