Maybe I’m being too dismissive, but this strikes me as an equivalent of existing-invention-but-using-a-computer software patents. I just don’t see how it’s particularly newsworthy or interesting that an image shared on Twitter was involved in the discovery. It allowed for a headline that made me click, though.
This fungus is exactly the sort of thing which would normally go missing in the vaults of a museum because the five people who ever saw it didn't recognise it as anything interesting. This is such a common phenomenon that trawling through museum collections is a non-trivial source of new species identifications.
The fact that an image normally only seen by a few people should be shared to thousands, and hence a discovery made based on it, is significant because there were few avenues by which it could happen pre-social media.