Remco Evenepoel is indeed the second-placed rider in the Young Rider classification, behind the overall race leader Lenny Martinez. However, there’s a specific reason why he won’t be wearing the White Young Rider’s jersey in the seventh stage.
In this case, it’s due to the Belgian national champion’s jersey that Evenepoel also possesses. According to UCI regulations (article 2.6.018), national champion jerseys are an exception to the rule of wearing classification jerseys if a rider is not the true leader. So, Evenepoel will be wearing his Belgian national champion’s jersey instead of the White Young Rider’s jersey in the seventh stage.
This exception allows national champions to wear their national champion’s jersey even if they hold another classification jersey.
Therefore, the Soudal Quick-Step leader hands over the white jersey to Juan Ayuso, the current third-ranked young rider.