I truly believe it is true. But if you look at it over longer time frame, it could change from 30 seconds. +ve 90% profit to 30 days. -ve 900% profit always measure how good the system is over long period of time.
I am sure that 99.99999% of all bitcoin traders did not made that trade. But theoretically it was possible. Reality is however not equal to theoretically. There surely are also traders who lost that 90% in 30 seconds.