Ignoring the fact the person was about to endanger people by hitting without being sure the shot was clear.... the actual rule depends on the local rule which I do not know for that course.
The ball technically is NOT out of bounds by the rules of golf if it is on course property.
I am assuming he was back on the course property across the street. You would need a local rule to address this.
This exact situation is addressed in decision 27/20 at the site:
USGA: Handicap Manual
27/20
Public Road Defined as Out of Bounds Divides Course; Status of Ball Crossing Road
Q. A public road defined as out of bounds divides a course. A ball crosses the road and comes to rest on the part of the course on the other side of the road. Is the ball out of bounds?
A. No. Since the ball lies on the course, it is in bounds unless a Local Rule provides otherwise.
However, because it is unfair that a ball on the road is out of bounds and a ball beyond it is in bounds, it is suggested that the following Local Rule should be adopted:
"A ball which crosses a public road defined as out of bounds and comes to rest beyond that road is out of bounds, even though it may lie on another part of the course."