If the goal was to make a work of art or a movie for a specific audience, then yes the numbers don’t matter.
If the goal was to alert the populace regarding the dangers of global warming and the need to take action now, then the numbers do matter.
I believe the movie was made for the latter purpose and your point about comparing the movie to others with an artistic intent or for a specific limited audience is not relevant. The movie is a failure if the purpose was to appeal to the masses.
The real goal for scare tactic documentaries is to feel superior. It provides a poster for all the principles to put in their office that shows they care. If the goal was to alert the populace then why open in only 4 theaters? To alert the populace you need to hit at least 1000 theaters.
I don’t give a crap about the artistic intent, I’m looking at the MARKET intent. You can tell a lot about what they wanted to do with a movie by it’s theatrical pattern. Opening in 4 theaters any time other than December is a clear market intent of not making a whole bunch of money (you get some tiny releases like that in December when movies are gunning for Oscars then a bigger release in January for the money). There’s simply no indication they thought this was going to be a cash cow of a movie, and if they didn’t think it was going to be a cash cow it’s hard to imagine they thought it was going to alert the populace, it’s hard for movies that don’t make any money to move the masses.