Or is it just bro science
Bro science. Exercise doesn't actually increase testosterone in the way you think.
It's only a temporary marginal increase that goes away completely like 30 mins post exercise. So if you squat 500lbs, 30 mins later the very small increase in test will basically be gone and your body will be back to baseline.
What does increase testosterone is a healthy bodyfat percentage + sleep + getting all of the nutrients your body needs.
Realistically, 8 hours of sleep a night + 10 mins (working sets) of strenuous exercise 3x a week + a varied healthy diet + a healthy bodyfat will literally maximize testosterone to the fullest a man can reach without steroids.
In fact, the more you train over this threshold the odds of your lowering your test will increase exponentially due to overtraining and increased recovery needs which are literally impossible to avoid without doping.