It's either UPNP being it's usual helpful self (i.e. too helpful and opening up everything), or people with absolutely no clue what they're doing and routing ports themselves.
There is *no* reason 99.9% of the printer owning population of the world would want or need their printer to be visible from the intertubes.
The 0.1% who do should be the ones who have to jump through hoops to do it and have it done properly (VPN).
The IoT is going to be a lot of fun for some people.