It could be both because in other Eddie alerts blood was not detected. Eddie was not put inside the car because Keela was searching for blood DNA evidence. A body was not in the car.
No body ... neither was there cadaver scent contaminant inside the car.
We have seen Eddie 'alerting' outside the car and to this day many still believe he alerted as a result of Madeleine's defrosting remains having been conveyed in the non-existent wheel well in the boot of the Renault.
We have seen Eddie Alerting inside Haute de la Garenne in Jersey. Some samples were recovered which justified his alerts ... but milk teeth do not evidence of mass murder make ... and that was the evidence that Lenny Harper was looking for.
We have seen Eddie 'alerting' in Luz ... and despite his handler's warning otherwise ... there are those who believe he was alerting to death. Which without corroboration is untenable. He may have alerted behind the couch and in the garage to a confirmed substance ... whatever else he barked at in Luz remains a mystery.
Perhaps more official effort should have been put into a Portuguese replication of the inquiry conducted into the failed Jersey inquiry which devoted a large part of its findings into the efforts of the cadaver dog and his handler.
The reluctance to sort it out may have been the ramifications of reviewing the conduct of the case in Luz and ignoring Figueira ... who knows?
However I think you have hit the nail on the head when you say "A body was not in the car."
Nor was there anything other than a key fob to which Eddie could react as per his early training to blood.