The non-B&S scenarios seem unreasonable...
The position was open at the start of the interview, but closed during the interview and they felt bad so considered him for a lower position:
but didn't mention that this happened and were going to ignore such a huge thing having happened. Physically possible, but completely unreasonable to assume.
They did the interview for the L2, but the non-technical person decided to change the tech level without talking to a tech person. Also not reasonable, and possibly still B&S even if this is what happened.
Is there a scenario where someone applies for too senior of a position and could legitimately get offered something more junior? Yes, but it would be discussed, it would be open and honest, and it would happen at a technical level not a recruiter screening. It's insanely unlikely in the real world, but could happen. But it would never happen like this, where it was done by an unqualified person, silently with no one discussing it until called on for it.