That's incorrect. Matter-over-Thread absolutely does NOT require IPv6 on your router. Even Matter-over-WiFi will happily work in IPv4-only networks, as long as your router does not filter the IPv6 announcements.
Some routers can work as _relays_ between the Thread network and WiFi, but this is entirely optional.
Some routers can work as _relays_ between the Thread network and WiFi, but this is entirely optional.