You can double click the node to open it up and see how it works.
The custom node is creating the non random checker pattern, which animated over 5 frames of I’m not mistaken (going by memory).
The noise is a texture, which is fully static in screen space. In the past, I’ve replaced the texture with a flipbook of noise so I could animate it.
I’m not sure the end result was strictly better but it’s easy to do if you want to try it out. Just make a copy of the TAA node so you can experiment without messing up the original.