Interesting wording in the law...so what if I had had my gun, and instead of ordering him to leave, ordered him to the ground? Then could I be sued for wrongful imprisonment or something?
Trespass is a tricky area. You can't simply seize someone for being on your property. If that was the case you could lock up half your neighborhood. You can ask anyone to leave for any reason whatsoever, its your property. But if they refuse and lets say they aren't doing anything, just not leaving... call the law and let them deal with it.
When you make the decision to hold someone at gunpoint, it better be a situation where you were in fear of imminent bodily harm. Especially when outside your house, even if it is inside your fenced in yard.