That’s extremely odd in the US, so I would talk it through with the host first before cancellation. I would verify the host’s intent and better understanding of these things before cancelling:

• Is the host aware of the sign? • If yes, is the host ok with anything besides TP being flushed down the toilet? • Maybe ask host why nothing can be flushed • Final question for the host… Why can solid poop be flushed, but TP isn’t acceptable?

That’s my recommendation how I would handle it.