Half correct.From a laymans point of view black mould is caused by 'the building' & therefore it must be the 'responsibility' of the buildings owner.
Anyone who has ever tackled the problem of black mould will have learned that it isn't 'the building' that causes the problem, it is down to the way the building is used.
It's down to occupancy. Simple. It's also incredibly idiosyncratic. The reason Rigsby landlords are reluctant to rid their shítholes of the risk of mold, is it costs money.