It sounds like your friend managed to complete a circuit through this dude's hood or frame. It's the same as touching the jumper cable contacts together while it's hooked up to your car.
From past experience, I'd start by checking your wire harness. It sounds like you overloaded the voltage regulator. If your voltage regulator fries, nothing protects your wiring. It also allows WAY too much juice to reach the main fuse, which would cause it to blow. I'd also check your alternator to see if it's charging correctly. You may need to replace it.