In a typical news story about a dive accident, the reporter will refer to the diers using oxygen tanks, and can routinely infer that they really mean air or nitrox. That is not completely true in this case.
In some articles, yes, you can see that they really mean air, but in some cases it really could be oxygen. For example, they want to bring the oxygen levels in the room up a bit, and different reporters have said they are using air tanks and oxygen tanks. Either one would work. In some articles, the reporter has called them air tanks in one sentence and oxygen tanks in another, and it is possible that either could be accurate or inaccurate. People with good knowledge have reported seeing big green oxygen supply bottles outside the caves in some of the news clips.