[TomGuy]

Area being evacuated of people, so maybe there is something in the rental car.

[SarahW]

Probably someone just left a suitcase or backpack in the car....

Suspicious package, so they take the precaution of treating it like a bomb.

If it were rented by someone with a country of origin that has given us trouble, or has a name similar to a person of interest, extra caution would probably be taken.