I think its very exciting work and he clearly made an important finding in lichen biology. But, overturning would be if he found that it wasn't 2 organisms but just 1. The previous 2 organisms are still there, there just happens to also be another one that people missed. Everyone else wasn't wrong and the previous work hasn't been overturned, simply added to. This is the basis of most modern science. This doesn't take away from the importance of the work, simply that the headline is a bit click-baity.

The previous understanding of these organisms was fundamentally wrong (although partially right). I think it's very odd to be sawing on this idea that 'overturning' a scientific theory requires a complete negation of it.

(If your argument is that "overturning" should never be used to describe a scientific breakthrough you may have a point, albeit a rather uninteresting one.)

Did you read the entire article? The end of it goes into how many things we thought we knew about the previously-known fungus and algae may not be true after all, there's a lot of work that's going to have to be reevaluated.