Is this a true? You should use garlic with pork and ginger with beef and never vice versa?
Whether or not it's a good idea is subjective, but the Chinese seem to break that rule a lot!  For example, Northeastern Chinese sweet and sour pork (guō bāo ròu) is characterized by an intense ginger flavor.  The Sichuan classic twice cooked pork (huí guō ròu) calls for boiling the pork with ginger.  A common condiment for beef dishes/sauces is black bean garlic paste (蒜蓉豆豉酱).  Perhaps this saying is associated with a specific Chinese regional cuisine?