It wasn't a drain cover though

Well the formula 1 article refers to it as a drain cover. It did look more like a cap but since I don't know the technical term, I went with what the official article referred to it as.

If you put a shelf up onto a wall, and then when you load up the shelf the wall falls over. That's not on you.

It is on you if you are the one who designed the shelf and decided to fix it at point of the wall without measuring if the wall could handle the load. It is different matter if you had a carpenter to build and install the shelf. In that it is his/her responsibility to ensure that the wall can handle a loaded shelf. In this case, since FOM are hosting the race, it is completely their responsibility that shit like this does not happen.