You can put two and two together and figure out it was them. Months ago Sharon Osbourne announced that one of the bands from back to the beginning was removed from the lineup for wanting money.
Ozzy Osbourne's wife and manager Sharon has told Billboard that she was forced to remove one big name from the lineup of this weekend's "Back To The Beginning" charity concert because the artist in question "wanted to make a profit" from the event. "And it's not the time to make a profit," she...
blabbermouth.net
The only bands that was missing from the original lineup announcement were Soundgarden and Mammoth. Wolfgang as well has Van Halen himself have always been close to the Osbournes so we can rule out Mammoth
Soundgarden was invited to perform at
Black Sabbath's "Back to the Beginning" farewell concert but were unable to participate due to scheduling conflicts. The surviving members,
Kim Thayil,
Ben Shepherd, and
Matt Cameron, confirmed they received an invitation from the show's musical director,
Tom Morello, but were forced to decline due to prior commitments. They acknowledged the invitation and expressed their respect for Black Sabbath in a social media post
according to Blunt Magazine.
Their official statement won't address this obviously, there was speculation that it could have been Megadeth but Kelly Osbourne confirmed that it wasn't them.
Here is news about the soundgarden thing
https://blabbermouth.net/news/membe...cornell-with-king-ultramega-single-rusty-cage
Note in neither instance of Soundgarden are they actually playing under the name Soundgarden but its still the same music