It might be that they’re one novel thing he could both discern as a specific thing and pretty much completely understand what their purpose is once he started paying attention to them. Just about everything in a modern city is an unfamiliar thing tied to a large context of other unfamiliar things, so you’ll just zone out when you’re missing the context, but stairs and carpets are pretty much just stairs and carpets.
It might be that they’re one novel thing he could both discern as a specific thing and pretty much completely understand what their purpose is once he started paying attention to them. Just about everything in a modern city is an unfamiliar thing tied to a large context of other unfamiliar things, so you’ll just zone out when you’re missing the context, but stairs and carpets are pretty much just stairs and carpets.