They did not go to the end of the runway, the completely left it and turned on a sand coloured surface after leaving the black main runway.There are lights at the end to mark the end of the runway.
If you go to the Lodz airport web site there is a link to a pdf which shows the detail of the current runway, i would presume the captain had this.
At the end of the day they left one surface and tried to turn on one which was sand like in colour and unfortunately turned out to be sand, no one was hurt and hopefully a lesson was learnt. If in doubt, stop or ask, the next time some one might not be so lucky.
http://www.airport.lodz.pl/files/aip_1..pdf