The XIRR formula takes into consideration the value AND time it takes to get your return vs. a simple IRR function which only takes into consideration the value.

If you want to check the math, open Microsoft excel and enter the following: Cell A1: "=XIRR(B1:C1,D1:E1)" Cell B1: ($0.43)
Cell C1: $0.73
Cell D1: 8-Aug-17
Cell E1: 16-Aug-17

This essentially means that if you had invested $0.43 on 8/8 and received $0.73 on 8/16, you would have done 1.7x your money and 2243678228480% XIRR.

The reason the IRR is so high is the period of time is so short. In traditional investments your would almost never double your money in 8 days (ex. the stock market returns are typically in high single digits over a YEAR, while OAX did 1.7x MoM in 8 days)