People are crazy! Easy to think it was the surgery that "improved" the arm instead of the nearly year worth of intense rehabbing to strengthen the arm, shoulder and surrounding muscles. Plus you add in all the bullpens and tweaking of mechanics as well. Of course that is the real reason why there seems to be an increase not the replacement of the UCL (though if it was trashed it would likely help a bit having a fresh replacement).
In my son's case we are hoping for a bump in velocity but know if it comes it will be due to the rehab work and the natural maturation process from 15 to 17 yrs old by the time he pitches in a game again. Son was also 82-83 while hitting 85 on occasion before tearing apart his UCL. He'd be tickled pink to be hitting 87-88 after his surgery and rehab his junior year.