LOL, no. This is not the case. Cite your source.
Leg and core strength are the primary force generators for throwing velocity. The new elbow ligament does not create new leg strength, but the by product of a Tommy John Surgery rehab program is improved length strength that can yield new velo. In addition, players following TJ surgery & rehab tend to concentrate much more on developing great pitching mechanics. From a research analytical perspective, we say that Tommy John Surgery may be associated with increased velo, but Tommy John Surgery is not causal to increased velo.
What Does The Research Say For Professional Baseball?
For professional players already performing at the extreme limits of their velocity, velo may not go up after surgery. To better answer this, some colleagues and I conducted a study in 2014 that examined velocity in professional pitchers before and after Tommy John Surgery. When we compared 3 years prior to TJ with 3 years after TJ, there was no difference in fastball velocity for starting pitchers in Major League Baseball.
https://www.drahmadsportsmedicine.com/question-will-velocity-go-tommy-john-surgery/