The node being complained about isn’t “using” TTN anyway. That it shows up on a TTN gateway is essentially irrelevant - a tiny bit of back-haul traffic and server capacity gets spent passing the packet on and then discovering there is nothing to do in response.
Banning it at the gateway wouldn’t really change much - passing on traffic from foreign nodes is routine, and is not considered to be a problem. The actual problem would be th air capacity, but TTN gateway behavior has nothing to do with that.
Also most likely the reason it keeps issuing join requests is that nothing is responding to it - its strategy is of course broken to be continually issuing requests so frequently, but its traffic is essentially “is anyone there?”
With traffic that frequent you could potentially do some direction finding.
