It was a free sample order from The_Magic_School_Bus on AB to test his stuff. So it is definitely not a scam on his part. The worse thing is that he included a paper in it stating what the substance was and his seller name. That has to be the worse OPSEC. By the way my mailbox is locked by key so only the mailman and I have access to it.
First time something like that ever happened to me. I guess it would be safer now only to order stuff that are not shipped in letters? My other letters had not been opened / I had a normal package untouched.
WHAT.THE.FUCK.