The way I see it is if you keep dropping an item on purpose at spawn when there is always the risk of someone stealing it, then having it get stolen is somewhat your own fault. If sSteak had been trading the shulker's contents with someone and someone like Obstinance aggro pearled at it, then sure that's stealing, but when you knowingly drop the shulker multiple times besides someone you don't intend on giving the item to and they get hold of it, that's on you.
Why would it be on you? I could understand your argument if steak was repeatedly letting Obstinance pick up the shulker then demanding it back, but as I understand it Obstinance pearled onto a dropped shulker. And because it was dropped multiple times that should mean it's fair game? There's zero precedence for anything like that.
The other argument that steak was "trolling" and thus breaking the rules is completely irrelevant. Even if it was decided that he was breaking that rule, why would that steak lose his shulker box as a result? We don't punish players by taking items away in cases of inappropriately named items or /link spam, so doing so here would be wildly inconsistent.