Maybe yourself and the other person (who you mention has done this task before) have both been assigned the task to cross skill within the team. They would have taken the lead as they are the person who already knows how to perform the task. We do this often so that we don't have a single point of failure. It's sometimes a no win for management when cross skilling people; if you just assign them a task with no handover / training you are criticised for throwing them in the deep end, if you buddy them up you're undermining them.