That slide is wrong, it's stacked the same way HBM is, the key difference is that they don't use microbumps anymore and instead have a hybrid bond system using copper to copper bonding. Copper is a good thermal conductor and the via is going through the entire wafer which in turn means that they are forming an uninterrupted copper cylinder that goes through all the layers. It's as if they put heat pipes inside the chip.

https://www.appliedmaterials.com/us/en/semiconductor/markets...

Edit: According to some rumors, the copper pillars go diagonally through the Z-Angle Memory.