On page 29 of the PDF, in table 4 'Weapons,' the damage for Thrown Object is listed as -1 . Surely that's a typo and should actually be +1? I could also see an argument for it not doing any additional damage, but -1 just seems weird.

The examples of thrown objects are improvised weapons, hence the reason I think damage is -1. It's just a way to do damage at distance, but not an optimal way.

Don't forget as well, uncancelled successes equal a point of damage. So your throw would need to be good for it to hurt your target.

As the GM you could also give bonuses for other factors, e.g. throwing a rock at a zombie from the roof, +1 positive die.

It's mostly a modifier for ranged, remember when they were throwing vinyl's at the zombie in Shaun of the dead?? that's a prime example.