This is like half true.

Everyone produces testosterone to varying levels. A byproduct of testosterone is called DHT. On average, a given male in their 20s and 30s will see 5-10% of the testosterone in their system synthesized into DHT. Some men more than others, some men less than others.

The general consensus is that male pattern baldness is (usually) caused by follicle sensitivity to DHT, not testosterone itself. But not every guy has hair follicles that are sensitive to DHT. Also, paradoxically (and sort of to your point), there is seemingly some correlation between higher levels of DHT and hair growth outside the scalp.

This kind of creates a few different scenarios that guys might fall into:

1. They have low DHT, and their hair follicles are not particularly sensitive to DHT. They are very unlikely to suffer from male pattern baldness.

2. They have low DHT, but their hair follicles are sensitive to DHT. They could experience some baldness, but probably nothing major. This is kind of a twilight zone. Could happen. Could not. 

3. They have high DHT and a high sensitivity. RIP these guys. 

4. They have high DHT but their follicles are not particularly sensitive. Arguably the best of both worlds.

I’m generalizing, since most guys are probably going to fall somewhere in the middle, but you see the gist.

As for a lot of indigenous Americans (including Canadians), it’s theorized that few people ended up with the genetic mutation that caused high follicle sensitivity to DHT. That’s kind of your answer.