The breed has different levels of aloofness, that with possible fear stage.

I personally would not be giving treats to strangers, it may cause the issue to get worse.

I work more toward him just being used to being out and about ignoring strangers, once your dog does not care about being around people then slowly work toward meeting people.

I agree my Dobermanns were tolerant of strangers but not friendly, people would be quite miffed when they'd try to stroke them and they'd just move away. Dobermanns are aloof too, no bad thing when you think of what they were bred for. I think the treats should come from you when he's tolerant of people. Maybe start with people at a reasonable distance rather than in his face.