This ought to be as newsworthy as the headline "Gambler just made $120M using a strategy called 'bet it all on a horse with 20-1 odds"
Finance has been doing the same for ages, so these people may come from a very traditional finance background...
Obviously you can research the eth market and form a view but you can also research horse racing form and the odds themselves should be a fair calculation indicator if the betting market is working well - so it seems fair to suggest that this is in the same category as a horse racing bet.
This is unlikely to happen overnight (if they are finance pros, they do compute probabilistic models), leaving them time to unwind their position when situation changes.
This is basic margin math.