'allegedly' is superfluous here. It's unfortunate that editors have sacrificed literacy on the altar of legalism.
Technically the phone isn't wiped - what GrapheneOS apparently does in this case is to delete just the encryption keys (deleting all the files would take too long). So, theoretically, the data can still be retrieved if the encryption keys are restored.
Pretty sure this qualifies as destruction of data (at least it is a supported mechanism according to NIST data destruction guidelines.) I don’t have the link handy but I quick google should confirm
Technically it was the agent putting in the duress password that erased the phone.
The phone wouldn’t have been erased if it hadn’t been illegally searched.