Possibly the exception that proves the rule, or possibly your workouts are as intensive as you think a pro boxers are?

Also, if you lost 75 lbs, you were most likely significantly overweight. Excessive body fat produces some sort of estrogen, while working out helps produce testosterone. Less fat=higher concentrations of testosterone in your system.

Not to mention, I don't see very many energetic 75lbs overweight people.

Or hell...it could just be the fact that the change in your lifestyle helped spark something mentally and gave you a new drive in life...there's a million possibilities.