We don't know what downed it yet, so it's hard to say. Iran is hiding and rationing their offensive munitions, we know that, so it's not surprising when the number of drone and missile attacks spikes after weeks of bombing. That's part of the plan. But the ability to take down a US fighter jet is not something they are rationing- it's likely at the edge of their capabilities and they got lucky. If they could be knocking down more, they would be.