In summary:
(1) It's not an American thing at all. I was wrong.
(2) It's not new. I was wrong.
(3) It has its roots in authorities charging or threatening to charge someone with the act of trespassing. I learned something today :-)
TLDR: "I was trespassed" means "I was charged with the crime of trespassing" (or "threatened with being charged with the crime of tresapssing").
In summary:
(1) It's not an American thing at all. I was wrong.
(2) It's not new. I was wrong.
(3) It has its roots in authorities charging or threatening to charge someone with the act of trespassing. I learned something today :-)
TLDR: "I was trespassed" means "I was charged with the crime of trespassing" (or "threatened with being charged with the crime of tresapssing").