It is a question of fact as to the status of the ball. Any questions as to where the ball is would be directed to the committee. If an answer were not readily available, the player could play two balls. OB is marked with white stakes, white line, or something is identified on your rules sheet. Hazards are marked yellow or red
If it is not OB, the player would need to find his ball. If unable to find the ball, it's a lost ball and the player would have to proceed under R27-1. If the area was a hazard, doesn't sound like it from your description, the player could proceed under the hazard rule R26-1.
Hope this helps.