Muranno horn fuse blowing

Friend has a 2010 Murrano. About 6 months ago, had front end of car replaced, such as grill, radiator. Couple months later, horn fuse starts blowing.

Today, we looked at the horns. I am thinking they were miswired, because one horn has black wire attached to ground, and the other horn has green wire attached to ground. I reversed so that both horns have black wires on ground connection. Fuses are no longer blowing and all seems good.

First of all, am I correct that they were miswired, or is it normal to have the two horns wired opposite polarity of each other (one horn had green on top, black on bottom, other horn black on top, green on bottom)?

Also, I had both horns completely disconnected from the circuit, but still mounted in the car, and there is continuity between both connection terminals on both horns, and thus all terminals were also connected to ground. Is that normal?*