Neutral fiefs are slightly different than other fiefs to protect against people trying to abuse the raid feature. With PC fiefs you can attack if you have 1/3rd the number of troops garrisoned in said fief. So if 0 troops just population anyone can attack, if 4500 troops garrisoned would need 1500 troops to even initiate an attack. With AI fiefs to protect them from being raided repeatedly for free gear you need 1/3rd the population to even attack it. 2000 population means you need at minimum 667 troops to attack.
I believe the "lol" quoted earlier is because you don't have a donut's chances at a dieting convention of ever beating 2000 population with only 145 troops.
