Jesus. That sucks. The news had sounded so positive, feel terrible for him.
My guess is that he suffered another blood clot, given the abrupt change in news. They surely did an extensive “hypercoagulable workup (blood tests to for genetic predisposition to clotting) and found nothing the first time, leading to 6 months of blood thinners. Even if the (possible) second clot is again “idiopathic” (meaning the docs don’t know why), a second clot still requires lifelong anticoagulation (blood thinners).
The Trent Brown trade makes even more sense.