Well, GP compared the rules against real life and decided that they are different from real life, so they shouldn't be followed.

Chess rules are also different from real life, but people don't have any issues following them.

The question whether it was “well defined” doesn't come into play here, I think: the rules in the game tell you to ignore any overrides (such as that certain vehicles may be allowed in an emergency situation). And GP decided to ignore that part.

I think interesting discussion can be had even when respecting this rule. For example, I decided that a skate board is not a vehicle but a bike is.