I think there are some really interesting things about the original post and the responses

The poster clearly thought and believed the concealed item was shoe shine stuff.

You can argue that it could have been anything and you can argue about the possibility of danger (to the metal or to people) in that bottle but the issue for the person posting was that something was being concealed - not the nature of the item that was being concealed. There are similar posts about reporting unattended luggage and other things like that.

This is precisely why they call it terrorism - because people become so terrified they find it hard to make reasoned, logical outcome-based decisions. I kind of understand it, but I wish we could all take a deep breath and think the sequence through before acting.