Good for him. Pretty rare that it actually works. Same in CA, its an old law.
REQUIREMENTS FOR OBTAINING LAND BY ADVERSE POSSESSION
A trespasser is entitled to legal ownership of property if his occupation of the property is hostile, actual, open and notorious, exclusive and continuous for a period of years set by state statute. (We explain each of these terms below.) Some states, such as California, also require the trespasser to have paid the local property taxes on the land.(1) The time required, which varies from state to state, is usually twenty years. It can be as short as five years when the trespasser pays the property taxes.