I don't follow. The particles were never "true 3D" to begin with - not in Andrews tutorial, not in any version of AE. It's just an illusion and layer stacking order is all that matters. The particles only exist inside their own little 3D universe.
I see that the layer order is different in the two examples. There's a 2D layer between 3D layers, and that is rarely a good thing. You just need to observe things more closely.