There must be a reason. Why one was turned down and one was approved.Our local council defiantly does they passed planning for a 5 bed house with triple garage a year before they turned ours down which is on the same road due to that the traffic would increase and it's a single road we have horses etc so the traffic would be the same
Compare the delegated reports on both applications, if you can find no difference in policies and justification then I would feel you have the basis of an appeal.