300 tons in 8 hours is 20 pounds a second. That’s like 3 gal/s.

Amazing numbers, even a water pipe that carries that much is a lot, much less bouillon

Considering the energy requirements to boil off that much water (70tonnes * reduction ratio) and form factor - notably the lack of a tall evaporating column - I'd hazard that they are concentrating via reverse osmosis. So the inside probably looks something like:

Pump -> Heat Exchanger [Cold to Hot] -> heater (sanitize and start cooking the stock)

-> continuously stirred vessel or just a large volume of insulated tube (cook time set by volume of vessel/tubing)

-> the same Heat Exchanger [Hot to Cold]

-> Membrane Separator [probably but not necessarily a bunch of tubes] which splits into Product and effluent [more or less pure water]. This step is also popular in Maple Syrup production to cut down on boiling, which is slow, costly, and can degrade the product due to temperature.

  -> Product IBC cube
  -> Sewer drain

Plus a bunch of valves and instrumentation for control and monitoring.

Is vacuum distillation a thing in food production?

Probably, can't say I am an expert. For bouillon which presumptively[0] has a very high boiling point due to the high concentration of salts even with vacuum a pot-style distillation would probably[0] be fairly slow. A falling film evaporator would likely work well, but there doesn't appear[0] to be room in the container for one.

Going all the way to solid bouillon a spray-dryer would make sense, and would fit. Solids handling is usually a pita though.

[0]Sorry for the weasel-words: only my general, not specific, experience applies.