T28B,
I have no real knowledge of what happened, but I believe your suppositions are right in the first three statements. As for your question in item 4, I can only postulate that if it was an "innocent" event, someone felt it would be safer to discharge it (probably into the bin) before dumping the canister into the bin. My wife would do such lunacy, and that would not be the craziest thing I've seen her do. Before you ask, neither she nor I have ever been to LCY.
If it's not so innocent, I guess it could have been worse.