The first was caused by a heart defect called a PFO which is essentially a small whole in the heart which led to a blood clot. IANAD so I have no idea about the actual process or anything and don’t know whether this one is related but the first had nothing to do with concussions.
Just as a quick clarification, PFO (or patent foramen ovales) don't cause strokes. What happens is most clots in our body form in the venous system. Since veins return blood to the heart, if a clot were to break off in a vein and head elsewhere in the body, it would go vein, right side of the heart, lungs, and get stuck in the pulmonary artery which is why blood clots in the leg (DVTs) are often associated with pulmonary embolisms.
If someone has a hole in the heart, such as a PFO or ASD, that clot can go from veins to the right side of the heart then go to the left side of the heart through that hole and then enter the systemic circulation and make it's way to the brain. So the PFO was not what caused the clot, but it is the reason the clot went to his brain instead of his lungs.
Anyway I don't know the details surrounding this event obviously and adult neurology is not really my area of expertise but there have been some studies that suggest there is an increased risk of stroke after head injury/TBI/concussions. There's this study out of Taiwan from 2017 (
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5369066/) and then this NPR article from 2013 on the subject. As with most things in science it can't directly draw a line from A to B saying TBI causes increase risk of stroke, but the bottom line is the data I found in my very brief search suggests there people with TBIs/concussions have an increased risk of stroke.
Edit: link for NPR article
https://www.npr.org/sections/health-shots/2013/06/27/196217617/how-head-injuries-seem-to-affect-the-risk-for-stroke