It's not about a junior person leading in the decision, it is about deciding between competing solutions. As the senior person you should see the bigger picture beyond the current problem solution even if it's an area your unfamiliar with. The people proposing the solution need to convince you that their solution is the one to go with.

A good lead will listen to all sides, and explain how a decision is being made. The goal is that whatever decision occurs that everyone is okay with it, even if they disagree. This is where people skills (and engineering skills like cost, consistency, time) are just as important as technical skills.