Your Pi-hole is passing that request to its upstreams, and recently, the public fritz.box domain has come into owership by some obscure third-party, not by AVM (the manufacterer of FritzBox routers, see also Pi-Hole server only reachable by IP - #6 by Bucking_Horn).
Your debug log shows you've enabled Pi-hole's Conditional Forwarding via Settings | DNS, but didn't state a domain.
You have to add fritz.box as local domain.
Pi-hole would then forward your request to your FritzBox router, which would provide the correct answer.