The judge has no obligation to "determine where the Bowen Ranch property line is."
It is part of the legal obligation of the plaintiff to bring sufficient evidence into court to fully substantiate his/her claim. In this matter, that wasn't done. As a defense, Mike Castro simply told the judge that the damage was not done while the vehicle was parked upon his property.
It appears that the plaintiff was totally thrown and unprepared by this logical defense; and the plaintiff failed to substantiate with credible evidence that his vehicle was actually parked upon the Bowen Ranch.
In small claims, you're given one chance to prove your case. I believe that the plaintiff blew it by not being fully prepared. I suspect that Mike Castro won.