He did have the Fractal Define 7 Compact case, and the pictures[1] only show a single 140mm case fan. From personal experience the Fractal Define cases are great at sound reduction due to the thermal padding, but those pads also insulates well.
Given the motherboard and RAM will also generate quite some heat, if the case fan profile was conservative (he does mention he likes low noise), could be the insides got quite toasty.
Back when I got my 2080 Ti, I had this issue when gaming. The internal temps would get so hot due to the blanket effect of the padding I couldn't touch the components after a gaming session. Had to significantly tweak my fan profiles. His CPU at peak would generate about the same amount of heat as my 2080 Ti + CPU I had then, and I had the non-Compact case with two case fans.
[1]: https://michael.stapelberg.ch/posts/2025-05-15-my-2025-high-...