I have seen pictures of actual concrete stairs like that, many years ago.

Totally possible someone installed the form work for the stairs the wrong way and blocked off the lower ones.

Or they’ve mocked the building and instead of removing the old concrete stairs just walled them off like this.

Things like this are often a protest by the builders against the architect. They spot a problem with the design, try and tell them and get shouted at. They then build it to the design, knowing it's stupid, so the architect has to swallow the cost of fixing it.

It’s concrete.

Both stairs are perfectly usable on their own.