Smaller court size that Tokyo Olympics used is national regulation and not international regulation. It is in fact not legal according to ITTF (international table tennis federation). China's head coach has filed an official complaint, but...too late to do anything.

And no, Tokyo did not inform the anyone that the court will be smaller size. At least the Chinese delegation didn't know about it until they arrived. The Chinese athletes thought they were having mental problems until the coach took a ruler to the court and measured it to confirm that it is smaller than regulation size.