He apologized because he realized he was wrong. Not difficult not to believe that. After all colonialism shouldn't be glorified.
As I recall the Chinese people of Hong Kong had always been allowed to leave and move to the mainland.
So your logic isn't making too much sense since there was never a flood of people trying to get out..in fact it was the other way around.
In the late 90's before the handover there actually was a flood trying to get out...but they weren't heading for the mainland.