AssertionError shows up as an Event?

Question

This surprised me. In a lambda invocation, a failed assert shows up as an Event. I would have expected Alert:

"Msg": "IonLambdaException",
"Ex": {
    "Via": [
        {
            "Type": "java.lang.AssertionError",
            "Message": "Assert failed: (= (count s) 16)",
        }
    ],
    "Cause": "Assert failed: (= (count s) 16)"
},
"Type": "Event",
"Tid": 338,
"Timestamp": 162134781093