It may suit the Chinese Communist Party line to peddle this lie (designed, it seems, to reinforce their other lie that the Joint Declaration is China's business alone), but the historical reality is that the hopelessly outnumbered British and Commonwealth garrison fought bravely against the invaders for 16 days before, with no prospect of success, the then Hong Kong Governor reluctantly surrendered to avoid further loss of life. A visit to the military cemeteries at Sai Wan and Stanley would show Chen the graves of many of those courageous men he falsely labels cowards.
As it happens, the father (now deceased) of a friend was one of those who fought the Japanese here before enduring more than three years of brutality as a prisoner, initially in a local PoW camp then as a slave labourer in a factory in Japan. But apart from Hong Kong, Chen's statement is also a gross insult to all the British, Commonwealth and American servicemen who spent several years of their lives fighting against Japan. My own father was one of them, a signaller on a Royal Navy ship which saw action in the Far East. Without the efforts of those millions of men, it is quite probable that China today would still be under Japanese rule.
More on this story here and here.