All pihole installs would have defaulted to listening on the WAN interface. But that meteorite was averted.
To answer the OP, there is already a warning about it - "Make sure your pihole is firewalled". But first and foremost, the default config now never listens to WAN requests.
https://discourse.pi-hole.net/uploads/default/original/3X/d/d/ddfbce9c43144c750e6cd00b9ec7abe3d0afb85e.png
