> Tresspass is not a reflexive verb.

Correct. But it is, sometimes, a transitive verb. One can trespass (go somewhere one is not allowed), and one can be trespassed (be banned from a property). One can even be trespassed against, which has a different meaning altogether (to be wronged by someone else).

I think you and the other commenters are confused by the usage of “trespassing someone” because it’s not an everyday usage of the term. “Trespassing someone” is essentially shorthand for “formally banning someone.” Being formally banned from someplace (and notified of it) has special legal significance: it’s basically what determines whether you get kicked out (in the case of mere trespassing) versus getting arrested (criminal trespass). That’s why this phrasing is especially common among cops and other legal personnel.

> Saying someone got trespassed is like saying you were driven when you go somewhere in your car, or that the door opened itself; you're taking the agency away from the person doing the trespassing and saying that they didn't actually do it themselves, but rather someone else did it/it something that happened to them.

It’s not like that at all. The difference between “she trespassed” and “he trespassed her” is not the same as the difference between “the vase broke” and “she broke the vase,” even though both are examples of intransitive/transitive uses of a verb. Humans discussing trespassing in a legal context found it convenient for “trespass” to gain a new meaning when used transitively. This usage has now been around for decades so it’s not particularly new anymore, but it’s still uncommon because most people don’t have a need to talk about trespassing in a legal context, and notice of trespass in particular.