@anniejam I don't think how physically fit we are determines who gets an aneurysm. I think genetics play a huge role. It is simply a weakness in the artery wall. It can be triggered by consistently high blood pressure or by smoking or by obesity but not everyone who has high blood pressure or who has smoked or has been obese develops this condition.
We also need to remember that as a population, we are living much longer and medical science can find these abnormalities much more easily than in the past. Before CTs and MRIs, I think the only way to find the aneurysm was by autopsy. We are fortunate to be aware of our diagnosis while we are still kicking and have it monitored and repaired as necessary.
Afib can strike just about anyone, with or without an aneurysm repair. There are medications to treat that and also ablations of the heart muscle that is causing the afib. I wish your friend well.