I'm pretty sure it's actually just a continuous under extrusion. It becomes periodic in nature because material gathers under the nozzle and then it hits the blob from the previous layer and gets pulled off. It's a similar effect to how droplets form and fall off of your faucet when the flow rate is low. This also leads to the diagonal angles seen as the Z-height goes up.

It's usually hard to get this to happen consistently, which they've done quite well.

I've got no citations, but I worked in FDM Additive Manufacturing for a few years, and spent 4 months of that designing extruders for a name brand company.

What surprises me is quite how consistent it is. The blobs look perfectly consistent over thousands of layers, which seems very unlikely - even a tiny perturbation would grow bigger in each successive layer and eventually cause the blobs to be chaotic in nature, even if the first row was consistent.

I wouldn't be so sure, I saw a video of variable infill extrusion and it looked somewhat like this, although over a greater distance but otoh much faster. Speaking of which, it seems to be printing quite slowly.