Just to clarify, the TB4 injection isn't TGA approved, so would not be available as a subsidised treatment under the PBS.
Having another look at the articles, the three investigations ordered were blood tests, ECGs and echocardiograms.
I don't believe there is a specific blood test for TB4, and even if there was there would not be any meaningful level intervals available. If there was, I am almost certain it wouldn't be eligible for bulk billing. It is more likely they were tested for something more common. I have seen one study that say that thymomodulin may increase certain white blood cells - these can be easily tested for and are part of a routine blood test that is often bulk billed, so you could speculate this might have been one of the things they were looking at.
The other investigations would be clinically justified (and eligible for bulk billing) if there were concerns about the potential for heart complications. ECGs are regularly ordered as a routine investigation or as part of a standard physical, which wouldn't cause much concern. For example, if a doctor is considering starting someone on a drug that is known to have cardiac complications as a side effect, then it would be negligent for them not to order an ECG which would establish baseline heart function. However, the mass echocardiograms would be a lot harder to justify to Medicare for a group of young professional athletes given they aren't the most likely demographic to be suffering from heart conditions. I am only aware of one medication (clozapine - a specialised psych drug), that requires an echo as part of the initial treatment work up.