A competitor accidentally signed for the wrong solve attempt. This is considered a DNS according to Regulation A7c2):
A7c2) If the competitor signs (or otherwise marks) an attempt before they have begun it, they forfeit the attempt and the result will be considered DNS.
As the competitor was experienced enough, the Regulation A7g is not applicable. Therefore the WRC agreed to changed the original attempt to DNS.
The WRC would like encourage competitors to be familiar with the procedure of speedsolving (Article A). It is important to understand that the use of the signatures is not arbitrary but rather serves to identify the scramblers and judges and if the competitor agrees with the result.