IDK, I think finding a related cause would be reassuring. If you start seeing multiple sequential unrelated failures in a system you usually conclude the root cause is systemic.

Bad fuel isn't impossible. I'd just expect it to affect more than two aircraft. But if I also had two unrelated malfunctions in a fighter and a helicopter, I'm not jumping to conclude there's a systemic cause either. Sometimes lightning just strikes twice.

Now if two F/A-18s crashed, that's more suspicious and could indicate a systemic issue in F/A-18 maintenance or operations. But there's a large difference between a helo and a fighter. Different parts, different maintenance procedures.

Right, the worrying part is that the only thing in common is the ship's crew.

Overworked crews make mistakes; it happens. But when sailors decide a ship is unlucky, things get really bad.

Do you think it’s more likely that these are really unrelated compared to being common cause (for example bad fuel)?

Yes, because bad fuel would likely have affected a lot more of the air wing than just two aircraft. I'm sure they'll look into it, and it's a possibility. But it is also possible that those two aircraft just picked that time to break for unrelated reasons.