Mojang might be introducing cubic/vertical chunking system to Minecraft

So, I was watching this vid, and also checked for myself.

The error java.lang.ArrayIndexOutOfBoundsException: Index <number> out of bounds for length 24 means there are 24 elements - from number 0 to number 23 - of something, and whenever any entity is below or above the world height limits, the <number> in question becomes -1 and 24 respectively, which isn't in the array, so the game crashes.

so, the position in the array depends on an entities' vertical position; total world height is 384 blocks; 384 / 24 = 16;
meaning that 24 elements of the array in question probably correspond to (sub-)chunks placed on top of each other within the borders of "classical", 16x16x384 chunk; i.e. the world now actually consists of 16x16x16 chunks, with the Overworld being 24 these cubic chunks thicc.

when the player is in the lowest 24 blocks (-64 to -40), it's chunk number 0, when they are in -40 to -16, it's chunk number 1, and all the way to 296 to 320, which is chunk number 23. below and above would be chunks -1 and 24 respectively, leading to a crash

Now, why the change? my speculation is that they might plan to add a new dimension that spreads vertically instead of horizontally )or both?), for example, one accessible thru the "portal" in the Ancient Cities