If OpenAI's lawyers thought they were going to get away with it then OpenAI needs to get better lawyers.
This one is unique because Hauri (aka "Yung Gravy") is another music artist. The Midler case is actually mentioned in the court filings, too.
It's interesting to think about the blurry line between art and commercial products.
Part of being a good lawyer is sometimes "well, this didn't work in 1992 (or whatever) but it might fly now. Let's try it, worst case is X". And, as always, the devil is in the details.