Earlier quoted context omitted.
If you don't know what a soul is, and you think it's something people just make up, then you are missing out on the experience of being human and you have a bigger problem than not being able to understand what art is.
When you find yourself with a choice between "either this person doesn't understand the experience of being human or I'm not following what they mean" the latter is probably a sound choice.
It's my prerogative to determine, and it's fairly trivial to identify, the difference between someone who has trouble forming their thoughts into words, and someone who like this poster is clearly stating an antagonistic and divorced relationship with life itself.
I'm capable and free to judge. Your knee jerk reaction itself is highly suspicious and redolent of someone else who's going through a divorce with living.
You should always question your own interpretation. Yes. When you find some evidence that you may be misunderstanding someone, then yes, you should certainly default to giving them the benefit of the doubt and ask yourself whether you've misunderstood something. This is pretty basic ethics and rhetoric.
But the meaning of the poster was quite clear. It was absolutist, in fact, and it was nihilistic, derogatory and dismissive toward any notion of intrinsic human value. Wouldn't you agree?
My advice to you would be: When you find yourself intervening in a conversation to support something transparently antihumanistic and evil, by claiming without any basis or merit that the other party in the conversation is misunderstanding it, maybe you should assume that you're failing to understand something.