Anton Guzhevskiy, the chief operating officer at Australian cybersecurity firm ThreatDefence, also challenged Gerck to prove his claims. "I've shared an RSA-2048 public key and a corresponding private key encrypted by this public key. If you can decrypt the private key, you can sign some piece of text with it, which will prove that you are in possession of the private key," he said in a response to Gerck's post on LinkedIn. "Can you do it?"
"There is a publication delay, and I do not control that," Gerck responded.
Says it all really.
This sounds like CSW all over again. Ask for a signed message as proof, which would be trivially easy to provide if any of the claims were true, and instead be told that we have to wait for some paper or evidence to be published which will "totally prove it".

I won't be holding my breath.
I do not seem to understand how this challenge works.
In RSA you need the private key to decrypt anything that is encrypted by it by it. Now I don't know about encryption, but when you're signing something with the private key, the public key is exposed. But that doesn't really matter here because he also shared the public key by itself.
If something is "encrypted by the public key", that is by keypair and no password, right? Hopefully he did not use the public key as a pasword, because that would not make sense?