It's very possible that I'm wrong: obviously we don't have the knowledge of what their expectations from Stadia were, nor is it possible for anyone to now know how successful or not their Stadia launch would've been if Google had decided to keep trying to make Stadia work, nor do we know how many sales the game will get from this exposure.
But I still stand by my view despite agreeing with your first few sentences about the industry generally.
edit: It's mainly coming from gut instinct, so I've tried to think more about why my gut says that. I think the main thing is that the exposure is going to people who are interested in games industry business, or tech industry, or Google specifically. That's what everyone is discussing, not whether or not the game is actually worth playing (and unlike if it was some planned PR, there's not even any subtle suggestion within the story that the game is worth playing - nor to be fair that it's not worth playing).
Sure, a few people might click onto the steam page out of curiosity, or buy the game out of sympathy to the poor people getting screwed by this situation, but it would be surprising (to me at least) if the amount of people converting is more than if they actually just had a marketing person spend a day writing a piece of content for Hacker News / GamesIndustry.biz with the goal of being both interesting tech content and featuring mentions of what makes the game worth playing. And that's just thinking about doing targeted marketing to not-very-good target audiences (for promoting indie games - sure there are some areas where HN traffic is incredible and businesses that would love a front page post, indie games not so much).
SteamDB's data on the game doesn't seem to suggest that I'm wrong here, but maybe with time I'll become wrong. (Side note, while writing this comment I couldn't remember the name of the game we're talking about, so I had to go look it up... because the name of the game wasn't the interesting bit when I read about this earlier!) https://steamdb.info/app/1787630/graphs/