It means that Bitcoin Cash will be 300% more difficult to mine and be much much less profitable and will make BTC over twice as profitable

The fact that it says 300% must be a capped limit because it should be closer to a 600% increase but there is a maximum the difficulty can increase we will find out in a couple of hours what exactly will happen but expect miners to jump back over to BTC and a day or so after the bitcoin difficulty will drop a bit making it even more profitable