In french we call that a "pied de nez". "Turning the table" / "Poetic justice" / "Adding insult to injury" would all be more correct than "virtue signalling".
If there was no attacker and the company gave half a mil out of nowhere to a security company (or a charity) and boasted publicly about it, that would be virtue signalling.
But refusing to pay the ransom and giving the exact same amount to security researchers is just a big, giant, middle finger.
And a middle finger ain't no virtue signalling.