What happened?
I saw that there was a path below me. Thinking there might be a breakable hidden wall, my stubbornness brought me to Air Attack with the Faceless Spear Weapon twice, in a very short Intervall. I somehow hit the perfect angle to glitch myself through the wall in the provided image. I should not have glitched through that wall.
I will continue on playing for now and try to recreate the bug once I got to the same spot again, providing a proper step by step if I manage to recreate it.