I think there is a bit of disconnect between people knowing what is possible and what people fear might be doable.

It's entirely possible that there are good non technical reasons for believing who was behind this while being technically incorrect about what it was that they intended to do.

Some of the more fanciful notions might be unlikely. Some of the evidence is only relevent in context. The distance from the UN is not terribly compelling on its own, the significance of the area of potential impact containing the UN is only because of the timing.

A state action might be for what might seem to be quite mundane reasons. One possible scenario would be if a nation feared an action suddenly called for by other states and they just want to cause a disrupting delay to give them time to twist some arms. Disruptions to buy time like this are relatively common in politics, the unusual aspect would be taking a technical approach.

I felt like it was more likely to be a complete absence of a human in the loop.

Nitrogen oxygen at one atmosphere is a lifting gas on Venus. You could live in an enormous zorb if you can keep it sealed.

Not the argument. The elimination of life on earth can happen due to non human causes. An impact of the sort that created the moon would do the job.

Are there? Most places on earth have an established environment. There are things living in some very hostile to human areas.