I've run over this article on notebookcheck.com (in German) recently:
https://www.notebookcheck.com/Wenn-die-Adresszeile-zum-Affiliate-Link-wird-Opera-leitet-aktiv-Adresseingaben-um.1189846.0.html
And I think it's generally true: Opera isn't very transparent about ads and affiliate links in their browser. The article makes reference to the privacy statement but also shows that it's very general in some ways.
I've seen this behavior in mobile (Android) and desktop alike that you're sometimes referred to some promotional sites before being referred to the website you put into the address bar.
You can disable this behavior in the enhanced address bar on desktop, on Android I think you have to disable any suggestions. But it was there by default and even if I disabled all other promotional settings, it's there. So if you're unlike me you don't recognize and even disable things in the browser, you don't really know what's going on there. Leading to such bad press as this one.
I've also had two new tiles on my speed dial from Amazon and Booking this morning although I turned out "show suggestions". So my personal preference simply is ignored and overruled.
I know that Opera has to make money for its hard work and I'm willing to support it. But it's also about trust. Can I trust my browser not to do some shady things in the background I don't know about and I wouldn't agree if I knew.
In the process of installing when I go for further options I'm already asked about such things like promotional campaigns. It should be made a standard part in installation not be hidden in the options menu in my opinion. But it at least is transparent in a way. But I don't want to be "surprised'" later on by such hidden things, I would like to be asked. And I think it would also be the better way for Opera as well.
Trust can be destroyed and it may never come back, so why not building trust among their users? In the end, it's them and not easy money that keeps Opera going, isn't it?