They also multiplex across +200 channels across wavelength (wavelength division multiplexing).

Not sure what the baud rate of a single channel was in their experiment but probably between 32-80Gb which is common for the lab equipment at Universities. The industry is knocking on 100-400Gb where for the actual decoding and signal processing there is massive parallelism applied to reduce the rate even more

Unless I misunderstood, this is the number that matters. The 1+ Pb/s is like giving a headline grabbing statistic that highway can carry 10 million passengers per hour and then adding below that it's a 100 lane highway. The advancement seems that the de/multiplexing is done on a single module at each end.