Of course it was all part of a plan. Why else would the British have built a Gibraltar like-fortress at Singapore with the guns only facing out to sea? Like Churchill said: 'a battleship launched without a bottom.'
Actually the Japanese spent much of the early part of 1942 overwhelming second line troops and tiny colonial garrisons that had been stripped of much to their heavy weapons to fight the war in Europe. I wasn't until Guadalcanal and New Guinea when they got chewed up by well dug in and reinforced Allied troops that they really got a taste of what was to come.