Comment by evanelias

They didn't just "resell" and "integrate" this source code. Rather, they attempted to re-license it, despite not being the copyright holder in the first place. They have no legal right to remove or replace the original license.

They can build derivative works, and apply a new additional license on top, assuming the additional license is compatible with the original one, and the original one is retained for any unmodified portion of the original work. But they cannot legally remove the original license entirely, nor remove copyright/attribution from any code that they did not write.

Think about this more deeply: if permissive licenses allowed you to replace the license entirely at will with no restrictions, that would effectively mean the work is in the public domain. There would be no purpose to having any license text at all, if these licenses could be trivially removed and violated at will.