I'm very much in favour of shorter working days, but here is one way you can "pretend" to be less sick:

Being sick is not a binary. We've all had days wher we feel like shit but figure we don't feel quite ill enough to stay at home, and so end up taking a couple of painkillers and favourite source of caffeine and end up working.

Presumably the shorter the work day, the more likely you would be to consider it ok to push through it if you feel ill, especially if you have vested interest in demonstrating that a new arrangement like a 6 hour day "works".

I'm not saying they did, but there are many ways they could plausibly sustain something like that for quite a while. The question is whether it is sustainable on a long term basis, or if it would change if/when a 6 hour day is no longer an experiment.