What's wrong with running cars ads on his own websites? Unless he misled his visitors into thinking his site is official nissan motors website, I don't see anything wrong with running some ads on it.
Fortunately the courts didn't agree with your hypothesis. This is a clear-cut case of trademark violation.
If you owned apple.com and sold apples, all good. If you ran ads for computers and phones, it's a problem and infringing their mark.
Trademarks are supposed to protect a brand in the category they operate in. Using their name and profiting off ads for the same category is cybersquatting. He operated in a somewhat gray area trying to run a computer repair shop with ads and got forced to stop. There is a reasonable argument that running car ads on nissan.com, one of the largest known car brands could cause brand confusion.