Sukhbir Singh just commented:
Thank you everyone for the comments and suggestions. I just wanted to share that we have identified the app and will update this task tomorrow. (And yes, it is a mobile app.)
It lasted for a while, then apparently Google started to filter those sites; not the domains though as some of them resurfaced much down the first page. I highly doubt it's on my side as I'm using Waterfox with the usual well known privacy oriented addons, some of which could block suspicious pages from loading but none of them adds content that wasn't in the search results.
I just repeated the same search and got these:
I can reproduce his results instead, using the same search terms. The first results do actually look legit, but after the first 10-20 I see those useless links too. This however doesn't seem to be new, at least for me... I've seen that already when searching manuals for example.
Malware (specifically adware) browser extensions or malware on computer. Edit: I mentioned malware on ISP, but I guess Google has their TLS in order so the ISP shouldn't see or be able to mess with the content like they did before.
Not necessarily saying this happened on the user end though, I just outlined how it could happen.
