None of my Sonos speakers have ever seen an ethernet cable, only the diabolical rays of the wifi access point. All five come up connected via wifi as SonosZPs and have DHCP-issued IPs. I think it only creates a mesh if you use the boost feature with a cable. I guess that works analogous with my Arlo, where the cameras mesh with the base station which is wired into the LAN so it can talk to the internets and then Russian hackers can see me in my pants to my favourite selection of Miserable Girls Singing in Bathrooms.
It's just a bit of a mystery how they got onto a WPA-protected network with just, as far as I remember, the press of a button. It's a dark magic, for sure. Either that or I forgot the bit where the iPhone said 'share your password' when I was setting them up in which case there's probably not a lot of mystery to be solved.