This is how you get terrible infections. Dog saliva doesn't have healing properties. If your friend did this for anything more than a scrape he'd get blood poisoning.

Source: Had an open fracture on my ankle and then had the stiches pop open on my ankle while it was still swollen. They could not get it to close right so I had to deal with a silver dollar sized wound in the side of my foot for a month. I had a nurses show up at my house for wound therapy 4 times a week. Towards the end of it they had shown me enough that they only came by once s week to check on my progress and treat it themselves. I was expected and didn't mind doing my own first aid on it. Having a wound scraped out sucks so much and I refused to do that part if it needed it... Other than that you literally just need to keep it clean and let it dry out as much as possible. It will scab over and heal.

Note: they had to scrape it to get rid of something called proud flesh which is granular tissue that can build up and slow/prevent a wound from healing correctly.