If it seems really not normal the only thing I can think is maybe the food you are feeding is not fulfilling his dietary needs, but must say Kaiser will smell someone treating their dog at the park and go sniff and sit to get some and as I carry treats myself lots of dogs especially the Labs come and bother my pocket. Check out the quality of your food you are feeding at dogfoodadvisor.com and double check the amount you feed. Otherwise I find Basenji have very good noses and who could help themselves if they smell something yummy and forbidden. Problem can also be if people feed him at the park he will expect it, so If you see it I would ask nicely that they don't feed your dog just say he is on a special diet, if he learns he won't get anything it would help him to stop trying, maybe call him back to you and treat him yourself. Good luck.
Jolanda and Kaiser