Yeah my local post is the same way... Last year they opened up like 3 boxes I was sending live plants out in, because apparently a lot of people walk in with boxes of live pot plants and try to ship them or something.
And every time I went in with boxes they joked around asking if my plants were legal. So now I go to a different post office like 5 miles further from my place and they have never once questioned anything in any package I've sent out.
I really think it just depends on who's working and what branch you go to.
As for your luck Lawrence the seeds look nothing alike and wouldn't have matched the pictures they have. Whoever opened your package wanted those pepper seeds cause if they were legit Pot seeds with your address on them you would have been raided.