I remember there was a statement on the website about mining in the past. They claimed that they were mining bitcoin and they pay the 4.08% annual interest from the profit they make through mining.
They were probably lying and after some time, they removed that statement from the website.
The address they claimed received the mining payouts was
176sh81PQupUsFyX6hNL2PTYydSuL7Wu73 and if we look at its history they did receive over 4000 BTC, mostly coming from mining activity. The BTC was then sent to their old hot wallet address, so the story does check out. They seem to have discontinued after the payouts got too low.