I'm curious whether people think that in light of all their other lies, this might have been one too.

I'm confused about FUH's motivations. The alt accounts were being used to farm mana, but their other actions were often in wanton disregard for mana, giving away large quantities and making bad bets that FUh clearly knew to be bad bets, just for fun. (And FUH was very open about the fact that they didn't care about mana.)

This makes me think that they were primarily interested in popularity, since being seen as a good trader, and giving away lots of mana as gifts, are both things that get you status on Manifold. The steps challenge was something that made FUH seem very cool and the center of attention, so it seems possible that they faked it, but I'm not sure. They did post some photos, like of their pedometer, so it would need to be a somewhat elaborate fraud. But making 50+ alt accounts (and being as active as they were on them) also takes quite a lot of effort, so it's plausible.

But then again they seemed sincere in many ways, like their involvement in the Mechinterp server and challenges.

Overall I'm confused about why FUH behaved the way they did, don't have a great theory. I would be interested to hear others' thoughts.