Even if you’re only connected with your acquaintances, the algorithm ensures that many of the posts your connections like or comment on will show up in your newsfeed.

That's the bane of social media platforms where engagement is low (Twitter suffers from this too). There are very few content creators, and especial on a professional network, there isn't enough content generated to share daily, so to generate content, the platform needs to dig deeper into the bottom of the barrel and show you second-level engagement (ie friend of yours commented or liked some rando's content).