Glad to hear you had a successful ablation. That's really great news.
I mostly just have occasional PVCs but on some occasions have a run of them which becomes non-sustained ventricular tachycardia. Thankfully my heart is in good shape and it's actually caused by nerve signal "noise" from my vagus nerve and no actual defect in the heart's pathways. It took quite a while for my doctor's to puzzle it all out.
V-tach itself is usually very concerning because, as in Jiri's case, it went straight to ventricular fibrillation (where the heart's just quivering in an uncoordinated fashion and not actually pumping) and effectively stopped.
My guess is that Jiri has a genetic heart defect which makes him susceptible to sudden cardiac death (long QT syndrome, Brugada, etc). If he hasn't been cleared by now, I assume he has a diagnosis in hand and is likely an ICD candidate (if he hasn't gotten one implanted already).
It's scary stuff. I wish him nothing but the best.